What can free money tell us on the virtual black market?

"Real money trading" or "Gold farming" refers to a set of illicit practices for gathering and distributing virtual goods in online games for real money. Unlike previous work, we use network-wide economic interactions among in-game characters as a lens to monitor, detect and identify gold farming networks. Our work is based on a set of real in-game trade activity logs collected for one month in year 2010 from the world's second largest MMORPG called AION (with 3.4 million subscribers). This is the first work that empirically (i) shows that "free money network" is a promising measure/approximation for detecting and characterizing gold farming networks, and (ii) measures the size of the free money net and in-game virtual economy in a large-scale MMORPG in terms of the cash flow.