Google Inc, its YouTube video service, and Yahoo Inc on Thursday filed counterclaims against Xerox Corp in a lawsuit accusing them of infringing the document management company's patents on Internet searches.

In filings in Delaware federal court on Thursday, the defendants sought declarations that they did not infringe the two patents at issue, or variantly that the patents are invalid and thus cannot be enforced by Xerox. Xerox had sued Google, YouTube and Yahoo in February, claiming that Google services such as Google Maps, YouTube and AdSense advertising software, as well as Internet tools such as Yahoo Shopping, infringed two patents dating as far back as 2001. According to a court filing, Xerox contended its patents covered such technology as a system for generating queries for information relating to a document, and methods to integrate information from documents and other data. Xerox is seeking compensation for past infringements, and a ban on the defendants' use of the technology.