The patent, number 6,473,802, covers "cookie persistence," which makes it easier for a Web browser to resume an interrupted session on a Web site.
F5 said Wednesday it sued three competitors--Radware, NetScaler and Array Networks--for infringing the patent. The suits were filed in U.S. District Court in Seattle, the city where F5 is headquartered.
On Friday, Radware and NetScaler said their products don't infringe; Array Networks declined to comment until further review of the suit.
"Upon our preliminary review, we believe that the lawsuit is without merit and we intend to vigorously defend it. Further, we believe that the claims do not affect any technology that is core to our business," Radware Chief Executive Roy Zisapel said in a statement.
F5's patent covers technology that improves the interaction of servers and desktop computers with Web browsers. Information such as shopping cart contents is often stored in files called "cookies" on desktop computers; F5 was awarded a patent that lets a Web traffic management device reunite a desktop computer with a particular server if the desktop computer user returns to the Web site.
F5 has used the cookie persistence technology in its hardware since 1999. The company builds equipment used to balance a workload among numerous servers, a useful task in particular for large Web sites that use many servers to respond to heavy computing traffic.
The idea of seeking money from intellectual property assets is gaining in popularity among high-technology businesses. SCO Group, holder of Unix intellectual property originally developed at AT&T, has. And HP has begun a program to .
F5 benefited from the computing gear spending spree during the Internet go-go years, but. In the last quarter of 2002, F5 had net income of $520,000 on revenue of $27 million.