It's possible that these people played a badly stealthed game and didn't know it. COD World at War (Allstar release) was suppose to be improperly patched. Also, it's possible that these group of people played an early release of a game before the official launch of the game (or played a beta they weren't suppose to play).
Well... I know there have been bad rips out there, for sure. People need to learn to rip for themselves if they are going to use backups.
On the other hand, I know that there were a bunch of idiots out there with preview copies of games released before their time like... Gears 2 and Fallout 3.
If people are gonna play backups, they need to respect the process. Stay the hell off XBOX Live with it until the day it comes out. Don't go jumping on because you want to show off that you got new games to your friends.
You ruin the process for everybody! That's why they make an unmoddable XBOX 360, now. Because of fools that continue to do this.
There have been some reports of people that only play backups offline being banned. The supposed trap is that once you go online, any backups that were played offline attach their played status to the hard drive. Also, any achievements that were garnered during backup play offline would have to register to your GamerTag once you sign in.
Things like this can tell Microsoft whether or not you have the game before the intended retail date, what region the title may have come from, and give clues to Microsoft about the state of your system via the hardware ID.
A lot of guys I know have two systems. One for backup and one for LIVE play.