"... a criminal enterprise could open several thousand MMOG accounts. Each could be used to trade with other players in the purchase or sale of in-game assets, the funds from which would ultimately be withdrawn from the accounts. Since thousands of accounts may engage in millions of transactions, each with small profits or losses, it would be difficult to trace the true source of the funds when they are withdrawn. These transactions can be conducted worldwide without the oversight that typically accompanies international bank remittances. In fact, in February 2007, China's central bank and finance ministries called upon companies to stop trading QQ coins and virtual currencies, presumably to curb the unregulated exchange of currency."
I estimate that Symantec's solution to the problem is with greater security and client verification. However, a more simplistic approach would be taxation on virtual revenue, even if the concept is opposed by players. Think of it this way: Right now, income from sales in MMO games is supposed to be reported as ordinary income. Many people neglect to do this whatsoever. If, instead, there was automatic reporting to the IRS (or other country's tax agency, based on the residence of the player) of income derived from MMO sales, then the tax agency would know to expect payment from said individuals. Moreover, it ties a person to the MMO account, eliminating the possibility of spreading one person over 100 accounts and going unnoticed. Of course, this would have to be based on a cash out value, as has been suggested before by both myself and Bryan Camp. In any event, the process of losing money in the transaction generally makes different things less appealing as money laundering vehicles, and thus virtual taxation could be one answer to the problem.