Yahoo's suing Facebook over a series of patents, claiming the entire company is built on its technology.
In a complaint filed yesterday in a San Francisco court, Yahoo's asked for an order banning Facebook from infringing ten patents, covering everything from the customization of information to messaging.
The suit follows a threat two weeks ago from Yahoo, which demanded that Facebook start licensing the patents.
"Yahoo's patents relate to cutting edge innovations in online products, including in messaging, news feed generation, social commenting, advertising display, precenting click fraud, and privacy controls. Thee innovations dramatically improve user experience, privacy and security and enhance the ability of advertisers to connect with users," the complaint reads.
"Facebook's entire social network model, whcih allows users to create profiles for and connect with, amongst other things, persons and businesses, is based on Yahoo!'s patented social networking technology."
It points out that many other companies have already licensed the technology under dispute.
With an initial public offering looming, Facebook's going to be less willing than usual to have a patent case hanging over it, increasing Yahoo's chances of success.
Readers with long memories may recall that Yahoo did something awfully similar back in 2004, with a patent suit against Google - just as it, too, was preparing for an IPO. Google settled out of court, giving Yahoo $230 million worth of shares.