Speaking of MW2 backups is assumed to be piracy, even if claimed to be otherwise. It's just a probability thing, plus playing online before release may contradict the end user license agreement of the game.
I have noticed that recently flashed 360s tend to be more likely to evade bans. Maybe MS caught out a lot of people in a previous sweep but have allowed them to continue for marketing purposes.
Get them hooked on live, then ban. For more fees of course