ly quar- antine a virus or Internet worms within subnetworks [subnets]. By just installing a few such devices between subnets, a single device can protect thou- sands of users. By installing multiple devices at key locations throughout a network, large networks can be protected." Global Velocity, a St. Louis-based firm, has begun building commercial systems that use FPX technology. The company is working with corporations, universities, and the government to install systems in both local area and wide area networks. The device self-integrates into existing Gigabit Ethernet or Asynchronous Transfer Mode (ATM) networks. The FPX fits within a rack- mounted chassis that can be installed in any network closet. When a virus or worm is detected, the system can either silently drop the malicious traffic or generate a pop-up message on an end-user's computer. An administrator uses a simple Web-based interface to control and configure the system. 5.7 PUTTING A LID ON SPAM It's no secret that spam is spiraling out of control and that anti-spam filters do a generally poor job of blocking unwanted e-mail. In an effort to give e-mail users more control over spam, professors Richard Lipton and Wenke Lee of Georgia Tech's Information Security Center have created a new application that offers a different approach to reducing spam. "What does the spammer want the e-mail user to do?" asks Lee. "Usually, the spammer wants the recipient to click on a link to a Web address to find out more about the product or service and buy it online." In thinking about the problem from the spammer's point of view, Lee and Lipton realized that most spam e-mail contains a URL or Web address for potential customers to click. So they created a filter application based on looking for unwanted URL addresses in e-mails. "This approach and application is elegant and incredibly computer cheap and fast," says Lipton. "It seems to work better than the existing commercial products and the end user can customize it easily." Lee developed a working prototype ove