Making someone play a computer game seems like an odd punishment; but that's exactly what happened in one Chinese prison according to a former inmate.

In an interview with The Guardian in the U.K., Liu Dali a former inmate at the Jixi labour camp, said prison guards would make him and other prisoners play hours and hours of the popular role playing game, World of Warcraft. Liu and other prisoners would spend hours building up credits for the guards, collecting online currency which the guards would then be able trade for real money.

The practice is called gold farming and it reportedly earned the guards 5,000 to 6,000 renmibi ($770 to $925) per day. He says he and 300 others were forced to play the game 12 hours at a time. This would often come after days where Liu was forced to perform backbreaking labor including mining, carving chopsticks and toothpicks out of planks of wood until his hands were raw and assembling car seats.

If I couldn't complete my work quota, they would punish me physically. They would make me stand with my hands raised in the air and after I returned to my dormitory they would beat me with plastic pipes. We kept playing until we could barely see things, he said.

Liu was in the prison for four years from 2004 to 2007 for illegally petitioning the central government about corruption in his hometown. He says the money made from gold farming was even more lucrative than the backbreaking labor.

The credits earned from gold farming are traded to active gamers who will use them to buy virtual assets. The assets help the gamers complete the tasks within the game. World of Warcraft is one of the most popular roleplaying game for the PC. As of March 2011, it has 11.4 million subscribers according to Activision Blizzard, the game's publisher.

With the rising popularity of the game, gold farming has become widespread, especially in China. According to the China Internet Center 80 percent of gold farming for World of Warcraft is done in China. There are 100,000 full-time gold farmers in China alone. In 2009, $2 billion in virtual currency was traded in China. Even after Chinese government attempted to regular and stop the practice in 2009, people like Liu say they believe it still happens.

Many prisons across the north-east of China also forced inmates to play games. It must still be happening, Liu said.

Activision Blizzard did not respond to a request for comment.

Follow Gabriel Perna on Twitter at @GabrielSPerna