"Now, I’ve always hated the idea of software patents. But Yahoo assured us that their patent portfolio was a precautionary measure, to defend against patent trolls and others who might try to attack Yahoo with their own holdings. [...] I was naive. Even if the original intention was truly defensive, a patent portfolio can easily change hands, and a company can even more easily change its mind. Since I left in 2007, Yahoo has had three CEOs and a board overhaul."
http://www.wired.com/epicenter/2012/03/opinion-baio-yahoo-patent-lie/