Microsoft has disconnected thousands of Xbox Live gamers, claiming they have modified their consoles to play pirated games.
Reports suggest that as many as 600,000 accounts around the world have been disabled in the company's latest assault on piracy - although Microsoft refuses to confirm that figure.
Affected users no longer have access to Xbox Live, losing all online capabilities permanently - which means gamers looking to buy second-hand consoles should be careful.
The internet is awash with online sites offering mod chips and instructions, and attempts to get rid of them through the courts have been ineffective. Pirated copies of Modern Warfare 2 were available before the official launch.
"The health of the video game business depends on customers paying for the genuine products and services they receive from manufacturers, retailers, and the third parties that support them," said the spokesman.