By Jim Reed
Newsbeat technology reporter
Leaked copies of Grand Theft Auto IV have hit the internet, less than a week before the game's official release. Peer-to-peer download sites are listing what appears to be a full version of the Xbox 360 game. It is already top of one pirate site's download chart.
Files claiming to be the game have been posted online. In theory, users can burn it to DVD and play it on their console in the same way as a full-price release.
The game's creators, Rockstar, declined to comment.
Comments from downloaders suggest the pirated copy is working.
One wrote: "I've played it since this morning for approximately five hours. No freezes, no bugs, no problems."
But many users have criticised the leak.
One poster wrote: "There will be people sleeping on the streets just to get this game and you want to steal it. Whatever happened to buying the game and exploring it with your friends?"
Xbox 360 users have been warned they could be automatically banned from Microsoft's online gaming service if they try to play the game before it is available in the shops.
The first in-game footage from GTA IV has already been posted on YouTube and other video sharing sites.
Many of the clips have been removed by site administrators after a copyright complaint from Rockstar's parent company, Take 2 Games.
Record sales expected
Grand Theft Auto IV is widely expected to become one of the fastest selling console titles of all time when it is officially released on 29 April.
Rockstar has succeeded in keeping the game under wraps for more than a year.
Critics were not sent review copies and instead had to test it out at the company's headquarters.
The game was finally shipped to high street shops and other retailers earlier this week.