I was looking on the Digiex Xbox Live leader board and noticed some people have played games that are not out for a few months yet. I see people who have played Bayonetta which is not out for another 2 month and Modern Warfare 2 which is not out for another week or 2 yet How is this possible?
Bayonetta was released in Japan last week (the game is 100% English which is unusual for a game released in Japan first). As for Modern Warfare 2 its most likely people playing pirated copies as the game is all over the internet.
Modern Warfare was leaked about a week ago so as InsaneNutter said, they are most likely playing pirated copies.