A big launch can lead to big piracy, especially with the console version of Modern Warfare 2, which was available online for modded Xbox 360 systems for a week or more before launch. Microsoft knows you shouldn't be playing the game before its official release, and activity on Xbox Live gives them an easy target. Consequently, an unknown number of consoles have been permanently banned from Xbox Live.
The techniques Microsoft uses to separate those who have wrangled early copies of the game from retailers and pirates remain nebulous, but once a console has been banned from Xbox Live, the system is useless to anyone who wishes to play online. That's a problem-or an opportunity- for the second-hand market, as waves of banned consoles are now up for sale on eBay and craigslist.