• by Mark Walsh  @markfwal, March 12, 2012

Following up on its threat last month, Yahoo has filed a patent infringement suit against Facebook. The Web portal sued the social networking giant in federal court in San Jose, Calif. over 10 patents including methods and systems for online advertising.

The complaint comes as Facebook is preparing for an initial public offering this spring and echoes the patent litigation wars that have already hit the mobile industry involving companies including Apple, Microsoft, Samsung and Motorola.

"Unfortunately, the matter with Facebook remains unresolved and we are compelled to seek redress in federal court," Yahoo said in a statement released Monday. The company in February had said it would take action to protect its intellectual property if Facebook didn’t enter into a technology licensing agreement with Yahoo.

Responding to the patent lawsuit, Facebook stated, "We're disappointed that Yahoo, a longtime business partner of Facebook and a company that has substantially benefited from its association with Facebook, has decided to resort to litigation.  Once again, we learned of Yahoo's decision simultaneously with the media.  We will defend ourselves vigorously against these puzzling actions."

The Financial Times reported in February that Facebook has filed for 410 U.S. patent applications but currently holds only 56. The newspaper speculated that the lawsuit could  give Yahoo a bargaining advantage and potentially lead to it getting a stake in Facebook in advance of its highly anticipated IPO. The company is expected to command a valuation of up to $100 billion following its market debut.