Virtual worlds have become the newest tool for criminals to launder their ill-gotten gains.

According to a recent report by McAfee, cyber criminals are increasingly turning to the currencies in virtual worlds as a way to legitimise money earned from fraud, malware and other illegal activities.

Because cashflow is connected to user names, malware writers can convert funds from illegal activity into online currency for use in virtual worlds and then withdraw them again.

In the process, the criminal puts a step between themselves and the illegal act, thus creating legitimate or "laundered" money.

McAfee senior architect Dr Igor Muttik suggested that sites could help stem the flow by implementing a delay time between when a transaction in requested and when it is executed. Such a delay, says Muttik, could give law enforcement a chance to connect the flow of the criminal money.

Unfortunately, there are other ways for criminals to launder money in virtual worlds.

Muttik noted that because the sending of messages is free in online worlds, money can be reinvested into spam campaigns and laundered as revenue from those ventures.

To close the door on spam laundering, Muttik suggests that virtual world operators institute a small charge for messages. If each message cost a small amount of virtual currency, criminals would be less drawn to spam campaigns.

"As long as the price is not creating a negative, the bad guys can use dirty virtual money because sales of goods and services orchestrated by a spam campaign will clear their funds," explained Muttik.

"Unfortunately, a solution for raising the cost of virtual mail can only work as long as normal law-abiding players happily accept such a raise."