A keylogger-equipped worm that steals usernames and passwords from the massive medieval fantasy role-playing game, "Priston Tale," demonstrates the economic power of the virtual world, said a security firm Wednesday.

"This isn't just about doing better in a computer game," said Sophos technology consultant Graham Cluley in a statement. "Criminals are stealing virtual assets like armor, money, and weapons to trade for hard cash in the real world. We are seeing a trend of more battles between Internet gamers and malicious code to assist with this kind of robbery."

Dubbed "PrsKey.a" by Sophos, the worm waits for users to enter either Priston Tale or the Web-based Yahoo e-mail service, then starts capturing keypresses.

Like many other large-scale online games, Priston Tale is most popular in South Korea, but it also has players across Asia and in the U.S.

This isn't the first threat to online game players. Other e-worlds have been hit by worms and Trojans, said Sophos, including Lineage, Outwar, and Legend of Mir 2. And just last week, a Chinese exchange student was arrested in southern Japan for allegedly using bots -- automated characters -- to virtually "mug" Lineage II players, then sell the faux loot for real cash on eBay.