1. A web change-detection server comprising: (a) a processor executing instructions to implement an agent manager comprising an agent management interface configured for receiving Web Change Detection (WCD) agent requests, wherein said agent manager is further configured for 1) sending a WCD agent to a client web browser depending on one or more local parameters and one or more remote parameters, and 2) processing said agent requests and using information stored in a WCD repository and information from said client web browser for determining a type of WCD agent to be sent, wherein said WCD agent is a web digester engine or a void agent configured to compute a web-page summary and send said web-page summary to said WCD server for monitoring, wherein said web digester engine computes said web-page summary by calculating a cryptographic hash on said web-page content to verify data integrity, and said cryptographic hash is a MD5 hash; (b) a processor executing instructions to implement a WCD detector configured for 1) receiving web page information sent by said WCD agent, 2) detecting modifications to said web page by retrieving WCD information stored on said WCD repository and comparing said WCD information stored on said WCD repository to said WCD information from said WCD agent, and 3) updating said web page information on said WCD repository; (c) a web traffic controller configured for allowing and disallowing access to said server by maintaining an index of security-based filtered IP addresses and URL addresses and a list of recent accesses for detecting distributed denial of service (DDoS); and (d) a memory storing said instructions to implement said agent manager and said WCD detector; wherein said server is configured to communicate with a search engine in a pull mode, push mode, or a combination thereof.