Thousands of gamers may have been cut off from Microsoft's online gaming service Xbox Live for modifying their consoles to play pirated games.
Online reports suggest that as many as 600,000 gamers may have been affected. Microsoft confirmed that it had banned a "small percentage" of the 20 million Xbox Live users worldwide.
Microsoft said that modifying an Xbox 360 console "violates" the service's "terms of use" and would result in a player being disconnected.
"All consumers should know that piracy is illegal and that modifying their Xbox 360 console to play pirated discs violates the Xbox Live terms of use, will void their warranty and result in a ban from Xbox Live," Microsoft has said in a statement.
"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."
Many gamers modify their consoles by installing new chips or software that allows them to run unofficial programs. Some chips are specifically designed to play pirated games.
Microsoft has not said how it was able to determine which gamers to disconnect.
"We do not reveal specifics, but can say that all consoles have been verified to have violated the terms of use," the firm said in a statement.
Affected gamers were met with a message during the login process. It read: ""Your console has been banned from Xbox".
Reports suggest that the ban does not stop the console from working and only affects a gamer's Xbox Live account.
Industry figures suggest that piracy may cost the video game industry as much as £750m a year.
In other news, a UK court has dismissed a man's appeal against an earlier conviction for selling modification chips - "modchips" that allow gamers to play illegal games.
Christopher Gillham's earlier conviction was upheld by Hereford Crown Court which found that playing counterfeit games on a modified console infringed copyrights.