Gold farming could be worth as much as USD 500 million, according to research carried out by the University of Manchester.
The report, written Professor Richard Heeks, head of the development informatics group, suggested that gold farming employs 400,000 people who earn an average of USD 145 (GBP 77) per month, worth about USD 500 million.
"I initially became aware of gold farming through my own games playing but assumed it was just a cottage industry," Heeks told the BBC. "In a way that is still true. It's just that instead of a few dozen cottages, there turn out to be tens of thousands."
Gold farming is where MMO players generate in-game currencies which they sell for real currency, often going against developers' and publishers' terms of service.