What is a surprising in the lawsuit is that Yahoo and Facebook have been on friendly terms. For instance, in 2010, the two companies partnered to bring Facebook games and status updates to Yahoo's search engine.

Facebook, noted that detail in its comment on the lawsuit. "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," said a Facebook spokeswoman in an email to Computerworld. "Once again, we learned of Yahoo's decision simultaneously with the media. We will defend ourselves vigorously against these puzzling actions."

Yahoo, for its part, contends it's only trying to protect itself.

"Yahoo has invested substantial resources in research and development through the years, which has resulted in numerous patented inventions of technology that other companies have licensed," said a Yahoo spokesperson in an email.

"These technologies are the foundation of our business that engages over 700 million monthly unique visitors and represent the spirit of innovation upon which Yahoo is built. Unfortunately, the matter with Facebook remains unresolved and we are compelled to seek redress in federal court. We are confident that we will prevail," the spokesperson said.