The original lawsuit filed in San Jose federal court last month are related to social networking technology, on online advertising as well as privacy and technology for customizing the information users see on a Web page.
Yahoo filed the suit against Facebook last month. Facebook countersued, claiming Yahoo was infringing on its patents. Facebook's claim filed in a San Francisco federal court early April claim Yahoo services such as the photostream and an activity feature in Yahoo's Flickr photo-sharing service infringed on a Facebook patent, among others.
Yahoo denies claims Friday that it was infringing on 10 of Facebook's patents and accuses Facebook of engaging in unfair tactics. Yahoo claims that Facebook violated an agreement between the two companies to notify each other of possible patent infringements before going to court.
Facebook has already acquired patents from Microsoft (AOL) and IBM in order to fortify its IP portfolio.