Research by Manchester University shows that the practice, known as gold-farming, is growing rapidly.
The industry, about 80% based in China, employs about 400,000 people who earn £77 per month on average.
The practice is flourishing despite efforts by games companies to crack down on the trade in virtual goods.
Big industry
Professor Richard Heeks, head of the development informatics group at Manchester who wrote the report, said gold farming had become a significant economic sector in many developing nations.
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