Yahoo enforces its patents against Facebook. According to the lawsuit, filed in Federal District Court in San Jose, Calif., Yahoo contended that Facebook had knowingly and improperly violated some of the company’s core intellectual properties. The patents, which were issued from 1999 to 2010, cover advertising, privacy, customization, social networking and messaging reported by the NYTimes

See a perspective from an unsuspecting inventor for Yahoo Patents  in an article titled, “A Patent Lie: How Yahoo Weaponized My Work.”