What online video game is being used by Chinese prisons as a method of slave labor?

Answer: World of Warcraft. According to the Guardian, former prisoner Liu Dali "says he was one of scores of prisoners forced to play online games to build up credits that prison guards would then trade for real money." Dali told the paper that he was among 300 prisoners who were made to work 12-hour shifts acquiring virtual currency that can be exchanged for real money. "It is known as 'gold farming,'" the article explains, which is "the practice of building up credits and online value through the monotonous repetition of basic tasks in online games such as World of Warcraft."