Facebook this week launched a countersuit against Yahoo!, alleging that the ailing online giant is infringing on 10 of its patents. The countersuit is in retaliation to a Yahoo! patent-infringement lawsuit against Facebook that was launched about two weeks ago.

"From the outset, we said we would defend ourselves vigorously against Yahoo!'s lawsuit," Facebook General Counsel Ted Ullyot said in a prepared 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 claims that Yahoo! infringes on its patents related to display advertising, content personalization, and photo sharing, and that up to 80 percent of Yahoo!'s revenues come as a result of this usage. It cites the Yahoo! property Flickr, which utilizes photostream and recent-activity functionality, as an example of infringement.

Yahoo! had previously tried to convince Facebook privately to license between 10 and 20 patented technologies it claimed Facebook was using but not paying for. When those efforts failed, it went public with the claims and then sued Facebook on March 12.

Yahoo! says the Facebook countersuit is spurious.

"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," a Yahoo! representative said.

The New York Times notes that Facebook's countersuit involves patents that were largely created outside the company. According to the publication, 8 of the 10 patents involved in the countersuit were originally invented by companies that were later purchased by Facebook, and several predate the creation of Facebook itself.

Of course, patent-infringement lawsuits have become increasingly common and disruptive in the hotly contested mobile market. But the Yahoo!/Facebook battles indicate that these legal actions won't just be confined to one tech market.