A recent Manchester University study on gold farming pegs it as a $500 million global market, where some 400,000 workers -- 80 percent of which are based in China -- earn an average of $145 per month.

Speaking with the BBC News, Manchester University's Richard Heeks compared the gold farming industry's size to India's outsourcing industry.

"The Indian software employment figure probably crossed the 400,000 mark in 2004 and is now closer to 900,000," he said. "Nonetheless, the two are still comparable in employment size, yet not at all in terms of profile."

The study, titled "Current Analysis and Future Research Agenda on 'Gold Farming': Real-World Production in Developing Countries for the Virtual Economies of Online Games," describes its "$500 million per year" prediction as a "best guess," taking into account subscription and employment data.

According to Heeks, the somewhat criminal nature of gold farming made it difficult to predict a definite number for the industry. "It seems unlikely to be less than $200 million per year, and it could well be more than $1 billion per year," he said.