Microsoft thinks Linux and UNIX are bad words. It seems gamers on XBox Live are prohibited from using gamertag mottos including "Linux" or "UNIX." Attempting to do so apparently evokes the following response:
Your motto contains inappropriate language. Please try again.
News.com blogger Matt Asay surmises that the prompt is most likely a Microsoft developer's idea of a good joke. Even so, he says, "it's childish in the extreme."