The maker of the popular video game Grand Theft Auto: San Andreas has halted production of its PC version and predicted the loss of sales worth several million dollars, following the re-rating of the title as ‘adults-only’.

The ESRB (Entertainment Software Rating Board) revised the game's rating yesterday amid controversy over sexually explicit material in the game, unlocked by a software modification allegedly created by hackers.

Trouble with GTA: San Andreas started shortly after the PC version was released in June. Someone posted Hot Coffee, a modification that allowed users to play sexually explicit mini-games on the title, on the internet.

This caused an uproar, culminating in a call by senator Hillary Clinton for increased legislation and stiffer penalties to keep violent or pornographic video games away from children. The New York senator also requested that the ESRB revise its rating for the game.

Games maker Take-Two Interactive Software faces the loss of revenue because stores in the US will no longer be allowed to sell GTA: San Andreas to anyone under 18. The revised rating may also cause video game makers to spend more on increasing security in their products to avoid similar tampering with software code.

The ESRB's decision to re-rate a game based on an unauthorised third-party modification presents a new challenge for parents, the entertainment industry and anyone who distributes or consumes digital content, said a Take-Two spokesperson.

Take-Two said the scenes enabled by the Hot Coffee modification are not playable in the retail version of the game unless a user downloads and installs the unauthorised software, thereby altering the original content of the game and violating the company's end-user licence agreement and intellectual property rights.

The company said it co-operated fully with the ESRB's investigation into Hot Coffee and will provide a software patch for current users of the game and parents to ensure versions cannot be modified. Take-Two will soon begin working on a version of GTA: San Andreas with enhanced security to prevent the modifications that led to the revised rating, the company said.

GTA: San Andreas was last year's best-selling game globally, according to market researcher NPD Group.