Most gamers are familiar with the practice of 'gold farming' - building up game credits in multiplayer games that are then sold on to other players.
But according to the UK's Guardian newspaper, the Chinese government has noticed this happening too - and realised that it could be a great deal more lucrative than sentencing criminals to hard labor.
The paper cites Liu Dali, who says he was forced to break rocks all day and play online games at night.
"Prison bosses made more money forcing inmates to play games than they do forcing people to do manual labour," Liu told the paper. "There were 300 prisoners forced to play games. We worked 12-hour shifts in the camp. I heard them say they could earn 5,000-6,000rmb [$765-$928] a day. We didn't see any of the money. The computers were never turned off."
He said that if players failed to earn enough credits, they would be punished by beatings.
Gold farming's not an new issue: as far back as 2005, games developers were banning players for the practice.
Recently, two University of Michigan students were investigated by the FBI, which accused them of "potentially fraudulent sales or purchases of virtual currency that people use to advance in the popular online role-playing game World of Warcraft".
But it seems the practice has now become big business for the Chinese government, with the China Internet Center estimating that nearly $2 billion worth of online credits were traded in the country in 2008.
One wonders how many players would be happy to buy credits if they knew how they were being generated.