An incomplete beta version of Sonic 4: Episode 2 was accidentally leaked onto Steam yesterday, with quite a number of users over on the Sonic Stadium forum getting their hands on it before someone noticed the mistake and pulled it back down.
Users appear to have really enjoyed what they played, despite some noticeable bugs. SEGA has cleared any talk of the game leak from their official forums.
Sonic 4: Episode 2 will drop this Summer for XBLA, PSN, PC and iOS.
Thanks to Kotaku.