All too familiar with hackers looking to exploit security flaws in its software, Microsoft Corp. warned video game developers on Monday that their PC games are now a target for criminals.

Popular massively multiplayer online games, such as World of Warcraft, have created a market for valuable game identities loaded with gold or other hard-earned forms of in-game currency that can be used to buy new weapons, magic spells or other trappings to advance within the game.

Using malware or software designed to infiltrate a computer system, hackers steal account information for users of MMO games and then sell off virtual gold, weapons and other items for real money.

Those of you who are working on massively multiplayer online games, organized crime is already looking at you, said Dave Weinstein, a Microsoft security development engineer at the company's Gamefest video game development conference.

In multiplayer online role-playing games, players assume a fictional character and take control of the character's actions and interact with other players in a virtual world. For World of Warcraft, a user buys the game software and then pays a monthly subscription rate to access the online world.

Online game accounts are already on sale in the black market next to stolen credit card accounts, fraudulent passports, fake work papers and other illegal items gathered by identity theft.

In fact, some game accounts can be worth up to $10,000.

For a lot of the customers out there, there is more store value on their MMO characters than there is on the credit card with which they pay for the account, said Weinstein.

The police are really good at understanding someone stole my credit card and ran up a lot of money. It's a lot harder to get them to buy into 'someone stole my magic sword.'