I doubt someone has made copies of the files and dispersed them over the internet not saying its impossible but its unlikely
All the demos were on the Xbox I thought? And made only for purposes at the expos they were showcased at (not to mention MQ/dragons toggled off).
There's always plenty of these "betas" going around before major game releases. I think I've seen ones for Diablo3, Asassin's Creed: Rev, and Batman: Arkham City. Don't trust em unless confirmed by BGS itself.