The installer for GameSpy Arcade 1.09, the main file exchange and gaming software of GameSpy.com, available from sites like CNET Networks Inc.'s CNET.O Download.com service, was infected with the Nimda virus twice this week, GameSpy Chief Executive Mark Surfas told Reuters.

Surfas said the virus infected one of their download servers for two hours on Tuesday and five hours Wednesday night, while they were performing routine service.

"We were doing some maintenance and we let our guard down," he said, adding that the company, which provides thousands of downloads every day, has never had a similar incident.

"This registers with us as a serious, serious error," he said. "We're pretty upset about it. This is not cool."

Surfas said a total of 3,100 infected files were served, and the company is in the process of notifying everyone who got an infected file and pointing them to free anti-virus tools that will disinfect their systems.

He also said the company has not received any reports of user suffering any damage from contracting the virus.

GameSpy.com is operated by GameSpy Industries of Irvine, California, which is best-known among gamers for providing the back-end infrastructure, like software and servers, to power popular online games like "Soldier of Fortune" and "Medal of Honor."

Two weeks ago, Microsoft Corp. MSFT.O revealed that the Korean-language version of its software for development of online services was also infected with the Nimda virus, though the company said the virus was dormant and in no danger of infecting anyone's computer.

Nimda, which first struck in September of last year, is estimated to have cost up to $500 million as corporations cleaned up their networks.

Most anti-virus software programs have had the ability to detect and eliminate Nimda since the outbreak.

By Ben Berkowitz