RELATED APPLICATIONS 
   The following patent application is related to the present application, is assigned to the assignee of this patent application, and is expressly incorporated by reference herein:
         U.S. patent application Ser. No. 09/040,813, entitled “System and Method for Software Licensing”, filed on Mar. 18, 1998.       

   TECHNICAL FIELD 
   This invention generally relates to the management and enforcement of software licenses, and, more particularly, to a system and methods for automatically managing and enforcing terminal server software licenses through a “leased license” approach. 
   BACKGROUND 
   Software licensing has historically been based on a “trust” model in which the user (i.e., licensee) is presumed to be honest and trustworthy and to abide by the terms of the license. Under the trust model, a software license typically accompanies a software product to explain the terms of use. For instance, the software license might dictate that the program code is to be installed on only one computer, and may be used to make one backup copy. 
   Common types of licenses include “shrink wrap” licenses, “online” licenses, and “site” licenses. A “shrink wrap” license is a license that accompanies each software product that is sold individually in a shrink-wrapped package through, for example, retail stores. The user is typically assumed to accept the terms of the shrink wrap license upon breaking the seal of the package, or the container that holds the disk itself. 
   An “online” license is one that accompanies software products that are downloaded online, such as from the Internet. The license is typically presented to the user prior to downloading the code. The user is presented with a choice to accept or reject the license. If the user accepts the license (e.g., by clicking an “Accept” button on the screen), the user is presumed to have accepted the terms of the license and the code is downloaded to the user&#39;s computer. 
   A “site” license is a single license that allows installation of multiple copies of software on many different computers at a particular site or many sites. It is commonly used to sell software to corporations, firms, or other entities having many computers. The purchaser pays for a certain number of copies (e.g., hundreds or thousands), and the site license enables the purchaser to install that number of copies on its computers. The site license is beneficial because the software vendor need not supply a large number of program disks, but merely supplies one or a few copies of the software and lets the purchaser install the copies without violating the agreement. 
   Unfortunately, enforcing each of the above licenses is impractical, if not impossible in certain situations. Users may, purposefully or inadvertently, make multiple copies of the software code and install it on more computers than the license allows. Yet, software vendors have difficulty monitoring these abuses because they occur in the privacy of the home or company. Thus, it is believed that the software industry loses a large percentage of revenues each year simply due to illegitimate use of software by the licensees. 
   Another problem with conventional software licensing practices concerns internal monitoring and bookkeeping on the part of large-site licensees. In most cases, the licensees want to comply with the terms of the software licenses, but are unable to adequately track the software as it is used throughout the site. For example, a large corporation might purchase several thousand copies of the software and begin installing the copies. However, computers and personnel change over time and it is difficult to centrally monitor how many copies have been installed, whether the copies have expired, whether they need upgrading, and so forth. 
   A type of “per-seat” or “per-device” software licensing is terminal server licensing, which provides remote clients with access to terminal server resources such as remotely executable software applications. Terminal server technology, such as that made available by the Windows® 2000 Terminal Services product from Microsoft Corporation of Redmond, Wash., allows a wide variety of different client computer devices including personal desktop computers, laptop computers, notebook computers, handheld computers, Apple Macintosh workstations, UNIX workstations, and the like, to remotely execute applications on a terminal server over virtually any type of network connection. Terminal server licensing permits the monitoring and distribution of purchased software licenses and thus prevents the abuse by users who would make multiple copies of software code and install it on more computers than a license allows. 
   One method of per-seat terminal server licensing involves the use of a licensing clearinghouse through which customers purchase software licenses which are sent to license servers that maintain an inventory of available software licenses. The license server is responsible for distributing the software licenses to individual clients. It monitors the software licenses that have been granted to clients and continues to distribute licenses as long as non-assigned licenses remain available. Once the supply of non-assigned licenses is exhausted, however, the license server can no longer grant licenses to the clients, and the customer must purchase additional licenses from the license clearinghouse. 
   Per-seat terminal server licensing is typically enforced (e.g., in the Windows® 2000 Terminal Services product) by putting a “ticket” onto a client machine that indicates the machine is licensed to access the terminal server. When an unlicensed machine talks to a terminal server, the terminal server attempts to get a license for the machine through the license server. The license server provides the “ticket” which gets pushed down onto the client machine, presumably to remain there permanently, so that whenever that particular client machine connects to a terminal server, the terminal server recognizes it as having a license because of its “ticket”. 
   Although this method of licensing avoids some of the problems encountered in the conventional software licensing schemes described above, such as the abuse by users who make multiple copies of software code and install it on more computers than a license allows, and difficulties with internal monitoring and bookkeeping on the part of large-site licensees, various disadvantages remain. 
   For example, loss of the per-seat licensing information, or the “ticket”, on a client machine, results in various problems. Loss of the “ticket” on a client machine may occur because of a hardware or software failure, but typically is the result of reinstalling the operating system, reformatting the hard drive, or otherwise refreshing the system prior to giving the machine to a new employee after a previous employee leaves. Once the client machine loses its “ticket”, and then attempts to access a terminal server, the terminal server won&#39;t recognize the machine as having a license and will attempt to get a new license from the license server. If the license server has available licenses, it will provide a new “ticket” for the client machine. If not, the machine will not be able to connect to the terminal server. At some point, due to employee turnover and other factors, this process leads to a depletion of a customer&#39;s available pool of purchased licenses. The result is that the customer must either purchase extra licenses and make them available on the license server, or attempt to recover the use of prior licenses which became unusable when the original client machines on which they resided were refreshed. The disadvantages of this licensing method therefore include multiple licenses being issued to the same client machine, customers paying for extra licenses which are not being used, and customers having to go through the manual and arduous task of contacting the license clearinghouse and having prior lost licenses made available again on the license server for distribution to client machines. 
   Accordingly, the need exists for a new approach in managing and enforcing per-seat terminal server software licenses that assists customers in monitoring their own compliance with licensing agreements, ensures that customers comply with licensing agreements, prevents customers from paying for extra licenses that are not needed, and automates the process of reviving lost licenses to avoid the manual task of reclaiming lost licensees through the license clearinghouse. 
   SUMMARY 
   This invention concerns a system and method for managing and enforcing software licenses through automating per-seat software licensing using a “leased license” approach. In addition to providing vendors with the assurance that purchasers are complying with software licenses, the invention maximizes a customer&#39;s use of purchased software licenses while eliminating the difficulties previously associated with a customer monitoring its own compliance with software licenses. 
   The invention provides a way to enforce permanent licenses automatically by repetitively expiring leased licenses and making those expired licenses available again for use by individual client computers. An exemplary system includes a licensing clearinghouse which generates valid software licenses, a license server which maintains and distributes an inventory of software licenses purchased from the licensing clearinghouse, and multiple clients located at or affiliated with a customer company or other customer entity. 
   Terminal servers may act as intermediaries for clients that might not have network connectivity to the license server. In addition to acting as common servers that provide resources to clients, terminal servers include the ability to facilitate connectivity to the license server for purposes of distributing software licenses to the clients. Individual clients include various computing devices, such as desktop personal computers, workstations, laptop computers, notebook computers, handheld PCs, and the like, in addition to simpler, low cost machines or terminal devices having limited local processing and local memory. 
   In an exemplary system, a company purchases software licenses through a licensing clearinghouse. A license generator at the licensing clearinghouse creates a license pack containing a set of one or more individual software licenses. The license generator verifies the license pack for installation on a license server and sends the license pack to the license server using standard communications. The license server is responsible for maintaining an inventory of software licenses that have been purchased from the licensing clearinghouse and distributing the licenses to individual clients. 
   In a first implementation of the invention, when a client connects to a terminal server, the terminal server determines whether the client has been issued a license. If the client has not been issued a license, the terminal server assists the client in obtaining a license from a license server. If a license server is not available, the client is denied access to the terminal server resources. Assuming a license server is available and has an available license, the license is issued and pushed down to the client. Although the license is a permanent license, the license server assigns a random expiration date to the license. Thereafter, each time the client connects to the terminal server prior to the expiration date of the license, the client is permitted access to the server. When the client connects to the terminal server on or after the expiration date, the terminal server submits a license request to the license server. If the license server has an available license, it issues the available license with a new expiration date, and pushes the license down to the client. If the license server does not have an available license, no license is issued, and the client is denied access to the terminal server. 
   In addition, the license server automatically returns the original license to its pool of available licenses on the expiration date of the license. Thus, in the first implementation of the invention, upon connecting with the terminal server on or after the expiration date, the client will be issued the same license it was originally issued having a new expiration date, and therefore maintain accessibility to the terminal server. A benefit of the invention is therefore made clear by the scenario in which the client computing device loses its original license due to, for example, wiping the hard drive when a new employee is assigned to the client computing device. Where prior licensing schemes require human intervention to reactivate the lost license, the invention automatically makes the lost license available again for use by a client on the expiration date of the license. 
   Additional and more comprehensive implementations of the invention facilitate a more realistic network computing environment in which numerous clients are vying for the available licenses from a license server&#39;s pool. A first example includes the license server issuing a temporary license to a client when the license server does not have an available permanent license. This situation arises when a client loses its permanent license prior to the license expiration date. In this case, when the client connects to a terminal server, the terminal server makes a license request to the license server, and the license server issues a temporary license with a temporary period which provides access to the terminal server for the client. Thereafter, each time this client connects to the terminal server during the temporary period, the terminal server requests a permanent license from the license server to replace the temporary license. Therefore, once the client&#39;s lost license reaches its expiration date and is automatically returned to the license server&#39;s available pool, the license server sets a new expiration date and pushes this same license down to the client the next time the client connects to the terminal server, thus replacing the client&#39;s temporary license. This assumes that the temporary license has not already been replaced by a new license prior to the expiration of the lost license. Only if the license server fails to acquire an available license by the end of the temporary period, will the client be denied access to the terminal server. Thus, as licenses from additional clients expire and are returned to the available pool, a given client will receive a license prior to the end of the temporary period, and not be denied access to the terminal server. 
   In yet another implementation, a license update period is additionally provided in which the terminal server assists a client in renewing the client&#39;s current permanent license prior to the expiration date of the license. During the update period, each time the client connects to the terminal server, the terminal server submits a license update request to the license server. If the issuing license server is available, it will recognize the client as already having a valid license which needs an updated expiration date. The license server will then update the expiration date and provide this “same” license back to the client. If the license server is not available, the client is permitted access to the terminal server since its current license has not yet expired. If the client has not renewed its license in this manner by the expiration date of the license, then the license server will provide a new license to the client as described above, and the client should continue to have terminal server access. 
   Thus, through leasing licenses to clients and continually expiring and releasing them in a way that nets out the overall distribution of purchased licenses, customers will not lose the use of licenses that are wiped off of client computers due to events such as employee turnovers, and vendors will be assured that their licenses are enforced since the licenses cannot be improperly transferred or otherwise violated. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The same reference numbers are used throughout the drawings to reference like components and features. 
       FIG. 1  illustrates an exemplary system for licensing software. 
       FIG. 2  illustrates an exemplary computing environment which is suitable for implementing various computing devices within the software licensing system. 
       FIG. 3  illustrates components within an exemplary software licensing system and various software and hardware elements included in the components. 
       FIG. 4A  is a flowchart illustrating the general method of managing and enforcing software licenses implemented by an exemplary software licensing system. 
       FIG. 4B  is a continuation of the  FIG. 4A  flowchart illustrating the general method of managing and enforcing software licenses implemented by an exemplary software licensing system. 
       FIG. 4C  is a continuation of the  FIG. 4A  flowchart illustrating the general method of managing and enforcing software licenses implemented by an exemplary software licensing system. 
   


   DETAILED DESCRIPTION 
   Exemplary System for Software Licensing 
     FIG. 1  illustrates an exemplary system  100  for licensing software in which the invention may be implemented. Aspects of the exemplary system  100  not fully developed in the following description are described in more detail in the co-pending patent application entitled, “System and Method for Software Licensing”, incorporated by reference above. 
   The system  100  has a licensing clearinghouse  102  that creates and issues valid software licenses to one or more companies, firms, agencies, or other entities, as represented by company  104 . In a particular embodiment, the clearinghouse  102  is a separate entity from the company  104 . Examples of the clearinghouse  102  include a software manufacturer, a software vendor, or a third party agent that is authorized to issue software licenses on behalf of the software manufacturer or vendor. 
   In general, the exemplary system  100  allows a company  104  to purchase software licenses through the licensing clearinghouse  102  so that it may run software on company servers or computers. A license generator  106  at the clearinghouse  102  creates a “license pack” containing a set of one or more individual software licenses. The license generator  106  sends the license pack to a license server  108  using standard communications, such as a data communication network (e.g., Internet) or a portable data medium (e.g., floppy diskette, CD-ROM, etc.). The license generator  106  prevents the license pack from being copied and installed on multiple license servers  108  through a method of assigning a unique ID to the license pack, associating the ID with a license server  108 , digitally signing the license pack, and encrypting the license pack with a license server&#39;s public key, as described in detail in the co-pending patent application entitled, “System and Method for Software Licensing”, incorporated by reference above. 
   The company  104  has at least one designated license server  108 . The license server  108  maintains an inventory of software licenses purchased from the licensing clearinghouse  102  and distributes the software licenses contained in the license pack to individual clients, as represented by clients  110 ( 1 )- 110 ( 6 ). The license server  108  monitors the software licenses that have been granted to clients  110  and generally distributes licenses to new clients  110  as long as it has available non-assigned licenses. 
   Because clients  110  might not have direct access to the license server  108 , one or more terminal servers, as represented by servers  112 ( 1 ) and  112 ( 2 ), can act as an intermediary for the clients  110 . Each terminal server  112  is a common server that provides conventional resources to the clients  110 . In addition, each terminal server  112  is coupled to the license server  108  to facilitate license distribution from the license server  108  to the clients  110 . 
   The clients  110  may be directly coupled to the terminal servers  112  via a LAN (local access network) or WAN (wide area network), as represented by clients  110 ( 1 )- 110 ( 4 ), or by any other communication link. Additionally, the clients  110  may be indirectly coupled to the terminal servers  112  through a dialup connection as represented by clients  110 ( 5 ) and  110 ( 6 ). 
   Exemplary Computer Used to Implement Servers and/or Clients 
   The license generator  106 , license server  108 , and terminal server  112  of  FIG. 1 , are preferably implemented as computer servers, such as Windows NT® operating system servers from Microsoft Corporation, or UNIX-based servers. It is noted however, that the license generator  106  and license server  108  may be implemented using other technologies, including mainframe technologies, as long as they share a secure, inter-operable communication mechanism such as remote procedure call (RPC). 
   Individual clients  110  may be implemented as various computing devices, such as desktop personal computers, workstations, laptop computers, notebook computers, handheld PCs, and the like. The clients  110  may further represent a terminal device, which is a low cost machine with limited local processing and local memory. The terminal device includes a display, a keyboard, an optional mouse, limited computer resources such as memory, and enough intelligence to connect to a terminal server  112 . The terminal device merely provides a connection point to the server-based processing. 
   The clients  110  might also represent a network-centric computer, such as a Network Computer (or NC) or a Net PC. 
     FIG. 2  illustrates an example of a computing environment  200  which is suitable for implementing, either fully or partially, computer and network architectures described herein, such as the client  110 , license generator  106 , license server  108 , and terminal server  112 . The exemplary computing environment  200  is only one example of a computing system, and is not intended to suggest any limitation as to the scope of use or functionality of the network architectures. Neither should the computing environment  200  be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary computing environment  200 . 
   The computer and network architectures can be implemented with numerous other general purpose or special purpose computing system environments or configurations. Examples of well known computing systems, environments, and/or configurations that may be suitable for use include, but are not limited to, personal computers, server computers, thin clients, thick clients, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like. 
   Caching user network access information may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Caching network access information may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices. 
   The computing environment  200  includes a general-purpose computing system in the form of a computer  202 . The components of computer  202  can include, but are not limited to, one or more processors or processing units  204 , a system memory  206 , and a system bus  208  that couples various system components including the processor  204  to the system memory  206 . 
   The system bus  208  represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. By way of example, such architectures can include an Industry Standard Architecture (ISA) bus, a Micro Channel Architecture (MCA) bus, an Enhanced ISA (EISA) bus, a Video Electronics Standards Association (VESA) local bus, and a Peripheral Component Interconnects (PCI) bus also known as a Mezzanine bus. 
   Computer system  202  typically includes a variety of computer readable media. Such media can be any available media that is accessible by computer  202  and includes both volatile and non-volatile media, removable and non-removable media. The system memory  206  includes computer readable media in the form of volatile memory, such as random access memory (RAM)  210 , and/or non-volatile memory, such as read only memory (ROM)  212 . A basic input/output system (BIOS)  214 , containing the basic routines that help to transfer information between elements within computer  202 , such as during start-up, is stored in ROM  212 . RAM  210  typically contains data and/or program modules that are immediately accessible to and/or presently operated on by the processing unit  204 . 
   Computer  202  can also include other removable/non-removable, volatile/non-volatile computer storage media. By way of example,  FIG. 5  illustrates a hard disk drive  216  for reading from and writing to a non-removable, non-volatile magnetic media (not shown), a magnetic disk drive  218  for reading from and writing to a removable, non-volatile magnetic disk  220  (e.g., a “floppy disk”), and an optical disk drive  222  for reading from and/or writing to a removable, non-volatile optical disk  224  such as a CD-ROM, DVD-ROM, or other optical media. The hard disk drive  216 , magnetic disk drive  218 , and optical disk drive  222  are each connected to the system bus  208  by one or more data media interfaces  226 . Alternatively, the hard disk drive  216 , magnetic disk drive  218 , and optical disk drive  222  can be connected to the system bus  208  by a SCSI interface (not shown). 
   The disk drives and their associated computer-readable media provide non-volatile storage of computer readable instructions, data structures, program modules, and other data for computer  202 . Although the example illustrates a hard disk  216 , a removable magnetic disk  220 , and a removable optical disk  224 , it is to be appreciated that other types of computer readable media which can store data that is accessible by a computer, such as magnetic cassettes or other magnetic storage devices, flash memory cards, CD-ROM, digital versatile disks (DVD) or other optical storage, random access memories (RAM), read only memories (ROM), electrically erasable programmable read-only memory (EEPROM), and the like, can also be utilized to implement the exemplary computing system and environment. 
   Any number of program modules can be stored on the hard disk  216 , magnetic disk  220 , optical disk  224 , ROM  212 , and/or RAM  210 , including by way of example, an operating system  226 , one or more application programs  228 , other program modules  230 , and program data  232 . Each of such operating system  226 , one or more application programs  228 , other program modules  230 , and program data  232  (or some combination thereof) may include an embodiment of a caching scheme for user network access information. 
   Computer system  202  can include a variety of computer readable media identified as communication media. Communication media typically embodies computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared, and other wireless media. Combinations of any of the above are also included within the scope of computer readable media. 
   A user can enter commands and information into computer system  202  via input devices such as a keyboard  234  and a pointing device  236  (e.g., a “mouse”). Other input devices  238  (not shown specifically) may include a microphone, joystick, game pad, satellite dish, serial port, scanner, and/or the like. These and other input devices are connected to the processing unit  604  via input/output interfaces  240  that are coupled to the system bus  208 , but may be connected by other interface and bus structures, such as a parallel port, game port, or a universal serial bus (USB). 
   A monitor  242  or other type of display device can also be connected to the system bus  208  via an interface, such as a video adapter  244 . In addition to the monitor  242 , other output peripheral devices can include components such as speakers (not shown) and a printer  246  which can be connected to computer  202  via the input/output interfaces  240 . 
   Computer  202  can operate in a networked environment using logical connections to one or more remote computers, such as a remote computing device  248 . By way of example, the remote computing device  248  can be a personal computer, portable computer, a server, a router, a network computer, a peer device or other common network node, and the like. The remote computing device  248  is illustrated as a portable computer that can include many or all of the elements and features described herein relative to computer system  202 . 
   Logical connections between computer  202  and the remote computer  248  are depicted as a local area network (LAN)  250  and a general wide area network (WAN)  252 . Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets, and the Internet. When implemented in a LAN networking environment, the computer  202  is connected to a local network  250  via a network interface or adapter  254 . When implemented in a WAN networking environment, the computer  202  typically includes a modem  256  or other means for establishing communications over the wide network  252 . The modem  256 , which can be internal or external to computer  202 , can be connected to the system bus  208  via the input/output interfaces  240  or other appropriate mechanisms. It is to be appreciated that the illustrated network connections are exemplary and that other means of establishing communication link(s) between the computers  202  and  248  can be employed. 
   In a networked environment, such as that illustrated with computing environment  200 , program modules depicted relative to the computer  202 , or portions thereof, may be stored in a remote memory storage device. By way of example, remote application programs  258  reside on a memory device of remote computer  248 . For purposes of illustration, application programs and other executable program components, such as the operating system, are illustrated herein as discrete blocks, although it is recognized that such programs and components reside at various times in different storage components of the computer system  202 , and are executed by the data processor(s) of the computer. 
   Exemplary Architecture for Managing and Enforcing Software Licenses 
   The invention achieves management and enforcement of software licenses within the exemplary software licensing system  100  of  FIG. 1  through the exemplary software/hardware architecture  300  shown in  FIG. 3 .  FIG. 3  illustrates components of the exemplary software licensing system  100  and basic software and hardware architecture elements within these components which operate to implement the invention. The licensing system  100  components illustrated in  FIG. 3  include the license generator  106 , a license server  108 , a terminal server  112 , and a client  110 . The architecture elements shown within each of the system  100  components are a mechanism for facilitating the following functional description of the system  100  components, and are not meant to be a limitation of the architecture of any component. As noted above, the computing environment  200  of  FIG. 2  may be a suitable implementation of these system  100  components, but it is not the only possible implementation, nor is it intended to suggest any limitation as to the scope of use or functionality of the system  100  components. 
   In general, the license generator  106  produces software licenses for a fee, and the license server  108  consumes the licenses by installing them. The licenses are typically produced in license packs which each contain one or more licenses. The license server  108  can then distribute a license to a client  110 . This is usually, although not necessarily, done with the help of the terminal server  112 . The client  110  then uses the license to gain access to the resources provided by the terminal server  112 . 
   Referring to  FIG. 1 , the entity or company  104  that owns or is responsible for the license server  108 , registers itself with an independent certifying authority that is trusted by both the company  104  and the licensing clearinghouse  102 . The company  104  submits information identifying itself and various license servers  108  to the certifying authority. The certifying authority issues a certificate to the company  104  after verifying that the company  104  is a real entity and that the identification information is true and accurate. The certificate contains a public key of the company  104  (or particular license server  108 ), which is signed by the certifying authority. This certificate becomes the license server&#39;s  108  certificate which it uses when requesting a license pack from the licensing clearinghouse  102 . Similarly, the licensing clearinghouse  102  also registers with the certifying authority to receive a public certificate. The clearinghouse  102  certificate contains the clearinghouse&#39;s public key, signed by the certifying authority. Details of the registration and verification process through the certifying authority with respect to the company  104  (or its particular license server  108 ) and the licensing clearinghouse  102  are described in the co-pending patent application entitled, “System and Method for Software Licensing”, incorporated by reference above. 
   Referring now to  FIG. 3 , the license generator  106  includes processor(s)  302 , a master license database  304 , a license purchase module  306 , and a license producing module  308 . The license purchase module  306  executes on processor(s)  302  to receive a purchase request from the license server  108  to purchase software licenses. Typically the purchase request is for one or more software license packs. The purchase request includes information pertaining to the licenses and license server  108 . For example, the purchase request might contain such information as a license server ID, the license server&#39;s certificate (which contains the license server&#39;s public key), a client&#39;s platform type, the quantity of licenses desired, a product ID, and a list of features that the licenses should enable. Additional information about a company  104  (e.g., name, contract number, etc.) may also be requested for purposes of tracking and report generation. The license purchase module  306  stores this information in the master license database  304 . 
   In response to the request to purchase licenses, the license producing module  308  executes on processor(s)  302  to generate one or more license packs, each of which contains a set of one or more non-assigned software licenses purchased from the license clearinghouse  102 . The license generator  106  creates licensing packs and transports the licensing packs to the license server  108  in a secure way that prevents them from being copied and installed on multiple license servers  108  or being applied multiple times on the same server  108 . Details of the manner in which these security measures are accomplished can also be found in the co-pending patent application entitled, “System and Method for Software Licensing”, incorporated by reference above. 
   The license server  108  has a license installation module  310  which executes on processor(s)  312  to install the license pack(s) received from the license generator  106  on a database having an available license pool  314 . The license installation module  310  may also be used to order the license packs through the license purchase module  306 , when such purchase requests are made electronically. The license server  108  has a request handling module  316  which executes on processor(s)  312  to receive license requests from clients  110 , typically through a terminal server  112 . Upon receiving a license request, the request handling module  316  stores client identification information in an assigned license data pool  318 . This information, along with information on what licenses are assigned to a client  110 , determines whether a client  110  needs an update/renewal of its “same” license, issuance of a new license, or issuance of a temporary license. Upon receiving a license request, the request handling module  316  compares information from the requesting client  110  with information already stored in the assigned license data pool  318  to determine the license status of the client  110 . 
   The “same” license module  320  is called to execute on processor(s)  312  anytime a client  110  is recognized as either needing its current license updated, or needing a new license. Therefore, each time the license server  108  receives a request, the “same” license module  320  executes to determine if the client  110  has been previously licensed by accessing and comparing client identification and license status information previously stored in the assigned license pool database  318 . If the client has not been previously licensed, the new license module  322  provides a new license to the client  110  as described below. However, if the client has been previously licensed, and still possesses its license, the “same” license module  320  provides a new expiration date and reissues this “same” license to the client. This situation arises whenever a licensed client  110  accesses the terminal server  112  during a “license update period” prior to the expiration date of the client&#39;s license. Each license has a “license update period”, which is typically a period of about 7 days prior to the expiration date of a license in which current licenses are updated with new expiration dates and reissued to the same client. 
   In addition, if the client  110  has been previously licensed, but no longer possess its license, the “same” license module  320  will then search the available license pool  314  for this “same” license in order to update and reissue it to the client. If the “same” license cannot be found in the available license pool  314 , then the new license module  322  executes to provide a new license to the client  110 , as described below. 
   A previously licensed client  110  that no longer possesses its license, has either lost its license due to the client machine being refreshed (e.g. hard disk reformat, reinstallation, etc.), or it has not accessed a terminal server  112  during the “license update period”, and the license has expired. Expired licenses are returned to the available license pool  314  by the license clean-up module  324 . The license clean-up module  324  executes daily to review licenses in the assigned license pool  318  and return any assigned licenses to the available license pool  314  when they reach their expiration date. Therefore, when a client&#39;s license is lost, if that “same” license is not in the available license pool  314  when the client next accesses a terminal server  112 , then the license has either not reached its expiration date and has thus not been returned to the available pool  314  (illustrating that the license was lost), or, it has already reached its expiration date (without being “updated” during its “license update period”), has been returned to the available pool  314 , and has been reissued to a different client  110  that needed a license. 
   The new license module  322  executes to search the available license pool  314  for a new license which it provides to a client  110  whenever the client has never been issued a license, or whenever the client&#39;s “same” license is not available. Licenses in the available license pool  314  can be any available license. Therefore, any license previously issued to a client  110  that has been returned by the license clean-up module  324  to the available license pool  314  upon its expiration, is subject to being given to a different client. When a new license is available from the available license pool  314 , the new license module  322  sets an expiration date and issues the license to the requesting client  110 . When a new license is not available, a temporary license may be issued to the client  110  as discussed below. 
   The temporary license module  326  executes to provide a temporary license to a previously licensed client  110  which has lost its permanent license prior to the expiration date of the permanent license. The temporary license module  326  provides the temporary license when the client  110  is unable to have its “same” permanent license reissued, and is unable to have a new permanent license issued (i.e. no new licenses are available from the available license pool  314 ). The temporary licensing feature ensures that a company  104  does not have to purchase more licenses than it has clients  110  using the licenses. The temporary license module  326  accesses client identification and license status information from the assigned license pool database  318 , and determines whether the client has previously been issued a temporary license. If the client already has a temporary license, no temporary license is issued, and the client is permitted access to the terminal server  112  because the temporary period of the temporary period has not yet run out. If the client has not yet been issued a temporary license, then the temporary license module  326  issues a temporary license having a temporary period during which the client is permitted access to the terminal server  112 . Temporary licenses are non-renewable, and only one temporary license is issued to a client  110 . If the temporary period runs out prior to a client receiving either its “same” permanent license or a new permanent license from the available license pool  314 , then the client is thereafter denied access to the terminal server  112  until a permanent license becomes available. 
   The period of time over which the temporary license provides terminal server  112  access to a client  110 , for example, a 90 day period, is a reasonable period designed to allow long term management of the license server  108 . In addition, all permanent license expiration dates (i.e., for “same” licenses and new licenses) set as discussed above, are set to provide a permanent license period that is less than the temporary license period. In this way, the system ensures that prior issued permanent licenses which expire (e.g., because they are wiped from a client machine, or because a client does not access the terminal server  112  during the “license update period”), are returned to the available license pool  314  by the license clean-up module  324  in time to be re-issued to their previous client machines. 
   Therefore, in an exemplary implementation, all permanent license expiration dates are randomly selected to provide a licensing period which extends from 52 to 89 days beyond the date the license is issued or reissued. The randomized expiration date is used to prevent all the clients  110  from reaching their respective “license update periods” at the same time, and thus, results in an even distribution of the licensing load against the license server  108 . 
   The terminal server  112  architecture includes processor(s)  328 , a database having application programs and other resources  330 , an access module  332 , and a license request module  334 . The access module  332  executes on processor(s)  328  to permit or reject client  110  access to the resources  330  on the terminal server  112 . The access module  332  first determines whether a client  110  which connects to the terminal server  112  has been previously licensed. If a connecting client  110  has not been previously licensed, the license request module  334  executes to request a new license from the license server  108  for the client. If a new license is provided to the client  110  as discussed above, the client is granted access to the terminal server  112  by the access module  332 . Otherwise, client access to the terminal server  112  is rejected. 
   If a licensed client  110  connects to the terminal server  112  prior to the “license update period”, the access module  332  immediately permits access to the terminal server  112 . However, if a licensed client  110  connects to the terminal server  112  during the “license update period”, the license request module  334  is called to request an update to the client&#39;s  110  permanent license from the license server  108 . If the license server  108  is unavailable, the access module  332  permits access to the terminal server  112  anyway, since the client&#39;s permanent license has not yet expired. Otherwise, the license request module  334  requests an update to the client&#39;s permanent license from the license server  108 , which reissues the client&#39;s  110  “same” permanent license with an updated expiration date, as discussed above. The updated “same” license is pushed down to the client  110 , and the client is permitted access to the terminal server  112 . 
   The license request module  334  also initiates a request to the license server  108  when a previously licensed client  110  connects to the terminal server  112  on or after the expiration date of the client&#39;s permanent license. The license request made to the license server  108  should result in the issuance of the “same” permanent license or a new permanent license as discussed above, and the client should be granted access to the terminal server  112 . However, if a permanent license is not available from the license server  108 , the client  110  will be denied access to the terminal server  112  resources. Additionally, in the event a client  110  has previously been issued a temporary license, and the temporary period for the temporary license has run out, the client  110  will be denied access to the terminal server  112  resources if the “same” permanent license or a new permanent license is not available from the license server  108 . 
   Client  110  architecture includes processor(s)  336 , a license cache  338 , a remote application module  340 , and a browser module  342 . A client  110  wanting to access a terminal server  112  for resources or for remote execution of applications  330 , connects to the terminal server  112  through running a typical web browser  342 . Upon connecting with the terminal server  112 , if the client  110  possesses a license (i.e., a current license, an expired license, or a temporary license) in its license cache  338 , it presents the license to gain access to the terminal server  112 . The terminal server  112  evaluates the license as discussed above, and permits or denies access to the client  110  on this basis. Otherwise, if the client  110  is not licensed, and thus presents no license when connecting to the terminal server  112 , the terminal server  112  attempts to retrieve a new license for the client  110 , also as discussed above. Once the client  110  has access to the terminal server  112 , a remote application module  340  may execute on processor(s)  336  to run various applications  330  provided on the terminal server  112 . Although clients  110  may be implemented as many different kinds of computers, they only require enough processing  336  capability to connect to the terminal server  112  and implement the remote application module which facilitates the remote execution of applications  330  on the terminal server  112 . All the applications  330  run at the server with server-based processing. 
   Exemplary Method for Managing and Enforcing Software Licenses 
   Having introduced an exemplary software licensing system and architecture, an example method of operation will be presented with primary reference to  FIG. 4  (i.e.,  FIGS. 4A ,  4 B, and  4 C).  FIG. 4  is a flowchart illustrating the general method of managing and enforcing software licenses implemented by the exemplary software licensing system and architecture of  FIGS. 1 &amp; 3 . Specifically, the flowchart of  FIG. 4  illustrates this method at a beginning point which assumes that the license server  108  has already installed software licenses purchased from the license generator  106 , and thus does not illustrate transactions between the license generator  106  and license server  108  which are discussed above with respect to  FIG. 3 . To help clarify an overall exemplary method of operation, various operating scenarios will be individually described, each of which illustrates a portion of the overall method. 
   First of all however, as shown in  FIG. 4C , an ongoing aspect of the invention includes issuing permanent licenses with expiration dates to clients  110  and returning the licenses to an available license pool  314  on their expiration dates if they have not been updated. Thus, as illustrated by operations  450 ,  452 , and  454  of  FIG. 4C , a basic part of the overall method occurring on a daily basis, includes the license server  108  reviewing data in an assigned license pool  318  and returning any expiring licenses to the available license pool  314 . For example, a permanent license that is wiped off of a client machine (e.g., due to an employee turnover) will not end up having its expiration date updated, but instead will expire and be returned to the available license pool  314  on its expiration date. In such a case, if this client machine connects prior to the expiration date, it will be issued a temporary license, valid for a period of time which ensures that the client machine will be, ideally, issued the same permanent license once that same permanent license expires and is returned to the available license pool  314 . In order for this to occur, expiration dates for permanent licenses are set such that license periods are less than the length of the temporary periods provided by temporary licenses. An example would include setting the temporary license period to 90 days, while setting permanent license expiration dates so that all permanent licenses expire randomly between 52 and 89 days after the date they are issued. This general concept of license expiration dates being set so that temporary license periods outlast permanent license periods, is true with respect to each of the scenarios discussed below. 
   Referring to  FIG. 4A , each scenario begins at operation  400  with a client  110  connecting to a terminal server  112  in an attempt to remotely execute applications  330  or otherwise access terminal server resources  330 . A first scenario involves a client  110  that has no license. Upon connection, the terminal server  112  determines at operation  402  whether the connecting client  110  has a license. Since the client  110  has no license, the terminal server  112  will assist the client  110  in retrieving a new license from the license server  108 . First, the terminal server  112  determines if the license server  108  is available at operation  404 . If the license server  108  is not available, the terminal server  112  rejects access by the client  110  at operation  406 , and the client  110  disconnects at operation  408 . However, if the license server  108  is available, the terminal server  112  submits a license request at operation  410 , which the license server  108  receives at operation  412  ( FIG. 4B ). At operation  414 , the license server  108  determines that the client  110  does not need a license update, but rather needs a new license. Therefore, the license server  108  locates a new permanent license in an available license pool  314  at operation  416 , and sets an expiration date for the new license and issues the new license to the client at operation  418 . Assuming at operation  414 , that the client  110  had previously been issued a license, but that the license had been lost, the license server  108  would first attempt to locate this “same” license in the available license pool  314  prior to searching for a new permanent license. However, in the current scenario there is no previously issued license, and the new permanent license is pushed down to the client  110  through the terminal server  112 . The client  110  is permitted terminal server access at operation  422  ( FIG. 4A ). The client  110  may then initiate remote terminal server applications  330  or otherwise access terminal server resources  330  within the limits of its license at operation  424 . 
   In the event the license server  108  is unable to locate a license in the available license pool  314  at operation  416  ( FIG. 4B ), the license server  108  determines whether the client  110  has been issued a temporary license at operation  426 . The license server  108  additionally determines at operation  427 , that the client  110  has not previously been issued a permanent license that has been expired. Since the client  110  has not been issued a temporary or permanent license in this first scenario, and a new permanent license is not available, the license server  108  will issue a temporary license to the client  110  at operation  428 . The temporary license is pushed down to the client  110  through the terminal server  112 , and the client  110  is permitted terminal server access at operation  422  ( FIG. 4A ). 
   A second scenario involves a client  110  that has recently received a permanent license which has not yet reached its expiration date, and which is in a period prior to a “license update period”. A “license update period” is a short predetermined period prior to the expiration date of a license, typically about a 7 day period, in which the terminal server  112  will attempt to have the license updated through the license server  108 . In the second scenario, a licensed client  110  connects to a terminal server  112  prior to the “license update period”. The terminal server  112  determines at operation  402 , that the connecting client  110  has previously been issued a permanent license. The terminal server  112  determines at operation  430  whether the client is connecting prior to the “license update period”. If this is true, as in the current scenario, the terminal server  112  permits access to the client  110  at operation  422 , and the client  110  may then initiate remote terminal server applications  330  or otherwise access terminal server resources  330  within the limits of its license at operation  424 . 
   A third scenario involves a client  110  that has recently received a permanent license which has not yet reached its expiration date, but which is within the “license update period”. The terminal server  112  determines at operation  402  that the connecting client  110  has been issued a license, and at operation  430 , that the client is not connecting prior to the “license update period”. At operation  432 , the terminal server  112  determines if the client is connecting during the “license update period”. Since, in the current scenario, the client  110  is connecting during the “license update period”, the terminal server  112  automatically tries to update the client&#39;s permanent license through the license server  108 . If the license server  108  is not available (operation  434 ), the terminal server  112  permits access to the client  110  at operation  422 , since it knows that the client license has not yet expired. The client  110  may then initiate remote terminal server applications  330  or otherwise access terminal server resources  330  within the limits of its license at operation  424 . 
   However, if the license server  108  is available (operation  434 ), the terminal server  112  automatically requests an update for the client license at operation  410 . The license server  108  receives the request at operation  412  ( FIG. 4B ), and determines at operation  414  that the client  110  already has a permanent license, and is thus requesting that its “same” permanent license be updated. The license server  108  therefore does not need to find a new license for the client  110 , but instead simply resets the expiration date and reissues the “same” license to the client  110  at operation  436 . The updated “same” license is pushed down to the client  110  through the terminal server  112 , and the client  110  is permitted terminal server access at operation  422 . 
   A fourth scenario involves a client  110  that has received a permanent license which is now either at or beyond its expiration date. This scenario arises when a previously licensed client  110  does not connect with a terminal server  112  while in possession of its license during the “license update period”. This can happen under at least two sets of circumstances. The first, and most common, is when an employee assigned to the licensed client machine  110 , leaves the company  104  or moves to a different position within the company  104 . The client machine  110  is then transferred to a replacement employee and its hard disk, containing the permanent license, is reformatted, reinstalled, or otherwise refreshed, such that the license is wiped off the machine. It is therefore not possible for the client machine  110  to connect with a terminal server  112  while in possession of its license during the “license update period”. The second set of circumstances is simply where an employee to whom the client machine  110  is assigned, does not connect with a terminal server  112  during the “license update period”, even though the license is still present on the client machine  110 . In either case, the permanent license reaches its expiration date. 
   In this fourth scenario, the terminal server  112  determines at operation  402  that the connecting client  110  has previously been licensed, that the connection is not prior to the “license update period” (operation  430 ), that the connection is not during the “license update period” (operation  432 ), and whether the connection is during the temporary period granted by a temporary license (operation  440 ). Under the current scenario, since the client  110  has not been issued a temporary license, the client  110  cannot be connecting during a temporary period granted by a temporary license. Therefore, the terminal server  112  knows that either the client&#39;s permanent license has expired, or the client has been issued a temporary license whose temporary period has run out. The terminal server  112  attempts to update the client&#39;s permanent license or retrieve a new permanent license through a request to the license server  108 . However, first the terminal server  112  checks to see if the license server  108  is available at operation  442 . If the license server  108  is not available, the terminal server  112  rejects access to the client  110  at operation  406 . 
   If the license server  108  is available (operation  442 ), the terminal server  112  automatically makes a license request at operation  410 . The license server  108  receives the request at operation  412  ( FIG. 4B ), and determines at operation  414  that the client  110  has been licensed before, but that its permanent license has expired. Therefore, the license server  108  searches the available license pool  314  and attempts to locate the client&#39;s expired or “same” permanent license (operation  414 ). If this “same” license has not been issued to a different client, it will be available in the available license pool  314  for updating and issuing to the same client. The license server  108  would therefore reset the expiration date and reissue the “same” license to the client  110  at operation  436 . The updated “same” license would then be pushed down to the client  110  through the terminal server  112  to the client  110 . 
   If the license server  108  is unable to locate the “same” permanent license (meaning that this license was already reissued to a different client), it then searches for any new permanent license (operation  416 ) in the available license pool  314  and issues a new license with a new expiration date at operation  418 . However, when a new license is not available, the license server  108  determines if the client has a temporary license, at operation  426 . If the client  110  has not yet been issued a temporary license, as in the current scenario, the license server  108  determines at operation  427  if the client&#39;s permanent license expired. If the client&#39;s permanent license has expired, as in the current scenario, no license is issued to the client  110  (operation  446 ), and the client is denied access to the terminal server  112  at operation  406  ( FIG. 4A ). If however, the client&#39;s permanent license had not yet expired, the license server  108  would know that the license was either in an update period, or had been lost. Since a permanent license is not available, the license server  108  would issue a temporary license with a temporary access period at operation  428 . The temporary license would be pushed down to the client  110  through the terminal server  112 , and the client  110  permitted terminal server access at operation  422 . 
   In a final scenario, a client  110  that has received a temporary license connects to the terminal server  112 . As similarly described above, the terminal server  112  determines at operation  402  that the connecting client  110  has previously been licensed, that the connection is not prior to the “license update period” (operation  430 ), that the connection is not during the “license update period” (operation  432 ), and whether or not the connection is during the temporary period granted by a temporary license (operation  440 ). Under the current scenario, the client  110  has been issued a temporary license, so the temporary period may still be good or it may have run out. Whether the client  110  connection is during the temporary period or after the temporary period, the terminal server  112  attempts to update the client&#39;s permanent license or retrieve a new permanent license through a request to the license server  108 . However, first the terminal server  112  checks to see if the license server  108  is available, through operation  442  if the connection is after the temporary period, or through operation  434  if the connection is during the temporary period. If the connection is after the temporary period and the license server  108  is not available (operation  442 ), the terminal server  112  rejects access to the client  110  at operation  406 . If the connection is during the temporary period and the license server  108  is not available (operation  434 ), the terminal server  112  permits access to the client  110  at operation  422 , since it knows the client  110  is still within the temporary period of its temporary license. 
   Whether the client  110  connection is during the temporary period or after the temporary period, if the license server  108  is available (operations  442  and  434 ), the terminal server  112  automatically makes a license request at operation  410 . The license server  108  receives the request at operation  412  ( FIG. 4B ), and determines at operation  414  that the client  110  has been licensed before, but that it now has a temporary license and therefore needs a permanent license. Therefore, the license server  108  searches the available license pool  314  and attempts to locate the client&#39;s “same” permanent license (operation  414 ). If this “same” license has not yet expired, it will not have been returned yet to the available license pool  314 , and thus will not be available. However, if this “same” license has expired but has not yet been issued to a different client, it will be available in the available license pool  314  for updating and issuing to this same client. The license server  108  would therefore reset the expiration date and reissue the “same” license to the client  110  at operation  436 . The updated “same” license would then be pushed down to the client  110  through the terminal server  112  to the client  110 . 
   If the license server  108  is unable to locate the “same” permanent license (meaning that this license has not yet expired, or, that it has expired but has already been reissued to a different client), it then searches for any new permanent license (operation  416 ) in the available license pool  314 , and issues a new license with a new expiration date at operation  418 . If a new license is not available, the license server  108  then determines, in this scenario, that the client  110  has a temporary license, at operation  426 . Since the client  110  already has a temporary license, no license is issued (operation  448 ), and the terminal server  112  permits access to the client  110  at operation  422 , since the client  110  is still within the temporary period of its temporary license. 
   Although the description above uses language that is specific to structural features and/or methodological acts, it is to be understood that the invention defined in the appended claims is not limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the invention.
A system and method for managing and enforcing software licenses through automating per-seat software licensing using a "leased license" approach provides vendors with the assurance that purchasers are complying with software licenses while maximizing a customer's use of purchased software licenses. Licenses are automatically enforced by expiring leased licenses and making the expired licenses available again for use by client computers. A system includes a licensing clearinghouse, a license server, clients, and terminal servers. A terminal server assists a client in obtaining a license with an expiration date from a license server, and helps maintain the client's license status through license requests to the license server. Licenses that expire are recycled and made available again to clients. Prior to expiring, licenses are automatically updated during a license update period, and if a license is lost, a temporary license is issued. After the license update period, clients may receive a license update or a new license. Temporary licenses are replaced with permanent licenses that are returned to the available license pool, thus netting out the overall distribution of purchased licenses and assuring that a customer's use of purchased licenses in not lost.