In a strongly worded rebuttal, Amazon.com has countersued IBM. The companies have charged each other with patent infringement. The countersuit, filed in the U.S. District Court for the Eastern District of Texas, denies that Amazon.com infringes IBM patents, seeks to invalidate some IBM patents and charges IBM with infringing on some Amazon.com patents. <A HREF="http://www.cio.com/blog_view.html?CID=27500">IBM illegally uses Amazon.com technology in WebSphere,</A> a widely deployed application server, as well as in IBM information management services and products, Amazon.com claims.