Well if you pre ordered from gog.com you most likely have already downloaded 90% of the game, we're just waiting for the final few megs to be available on the 17th. So chances are the leak is that with some piraty files thrown in.
Anyway, i'm paying for this. There's no excuse , not even "region restriction" and "not available in your country" [my main reasons for not paying for something] can be used now.