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According to an Adrenaline Vault story, Marvel is suing NCsoft and Cryptic Studios because of their MMORPG, City of Heroes. Why? "Marvel claims that that the game allows players to create characters which are too similar to the Hulk, X-Men, and other heroes from their comic book series, violating their trademarks."
In related news, Marvel also announced suits against major paper and pen manufacturers, as well as Crayola and various paint companies.