Facebook mounts an aggressive legal defense against Yahoo over patents Facebook is pushing back against Yahoo's new chief executive, Scott Thompson, above, who is taking an aggressive approach to reviving the struggling Internet company. Paul Sakuma / Associated Press / April 3, 2012 April 3, 2012, 11:58 a.m. Facebook is mounting an aggressive legal defense against Yahoo, claiming Yahoo is infringing on 10 of its patents. Yahoo sued Facebook for infringing its patents last month. "From the outset, we said we would defend ourselves vigorously against Yahoo's lawsuit, and today we filed our answer as well as counter-claims against Yahoo for infringing 10 of Facebook's patents," said Ted Ullyot, Facebook's general counsel in an emailed statement. While we are asserting patent claims of our own, we do so in response to Yahoo's short-sighted decision to attack one of its partners and prioritize litigation over innovation. Facebook's counterclaim filed in a San Francisco federal court Tuesday claims Yahoo services such as the photostream and a recent activity feature in Yahoo's Flickr photo-sharing service infringe on a Facebook patent, among others. Facebook, which is planning a $100-billion initial public stock offering next month, is pushing back against Yahoo's new chief executive, Scott Thompson, who is taking an aggressive approach to reviving the struggling Internet company. Yahoo is expected to announce thousands of layoffs Wednesday in a massive restructuring. In an emailed statement, a Yahoo spokesman said: "We have only just received Facebook's answer and counterclaims, but on their face we believe they are without merit and nothing more than a cynical attempt to distract from the weakness of its defense. As we have made clear from the outset, the unauthorized use of our patented technology is unacceptable and must be resolved appropriately. Other leading companies license these technologies, and Facebook must do the same or change the way it operates. We have proposed that Facebook join us in discussions to resolve the matter, but our overtures have been rejected. As a result, we are prepared to continue to seek redress through the courts. Facebook has warned investors that an "unfavorable outcome" in the patent dispute with Yahoo could have a material effect on its business. Facebook warns of possible 'unfavorable outcome' in Yahoo lawsuit It's a patent war: Yahoo sues Facebook for infringement Yahoo hires former PayPal head Scott Thompson as its chief executive