As far as I know there was one main patent -- 6,988,138 -- which was utter garbage and was invalidated in 2009. It was this patent which BlackBoard used to try

As far as I know there was one main patent -- 6,988,138 -- which was utter garbage and was invalidated in 2009. It was this patent which BlackBoard used to try to shut down a competitor named Desire2Learn in 2006. The invalidation forced Blackboard to retreat, and they've since been much quieter on the legal front.