Yahoo has long worked closely with Facebook, using the social network to power sign-up and login of its email service and Flickr. Just 11 days ago, Facebook congratulated Yahoo in a blog post noting its Open Graph protocol had helped Yahoo’s news reader app gain 25 million users, including 2 million each day, and more than 500,000 referrals a day. I doubt we’ll see such courtesies between these two anytime soon.

via Yahoo Stabs Facebook In The Back, Says Pay For Its Patents Or Get Sued | TechCrunch.