After years of positive relations, friendly blog posts, and referral traffic, Yahoo may have just been biding its time waiting to declare war on Facebook. Today it suddenly accused its former ally of infringing on 10-20 of its patents. It demands a settlement from Facebook or it says it will sue. The betrayer only warned Facebook privately once the New York Times had publicly published details passed to it by Yahoo. Though dastardly opportunistic, this patent trolling could produce a big windfall for Yahoo’s investors.