The attack code, which space news site SpaceRef.com identified Monday as "W32.Gammima.AG," infected at least one of the laptops used on the station, an international effort headlined by the U.S. and Russia. NASA spokesman Kelly Humphries declined to identify the malware, saying only that anti-virus software detected a worm on July 25.

The first public report of malware about the ISS was logged earlier this month, on Aug. 11. In NASA's daily status report on the station that day, the agency said. Sergey Volkov, the International Space Station (ISS) commander, was "working on the Russian RSS-2 laptop" and "ran digital photo flash cards from stowage through a virus check with the Norton AntiVirus application."

A week later, on Aug. 21 Volkov "checked another Russian laptop, today RSK-1, for software virus by scanning its hard drives and a photo disk."

The next day, Volkov transmitted antivirus scanning results from the laptop to Earth, and American astronaut Greg Chamitoff scanned another computer for possible infection. NASA also said in Friday's report that all laptops on board the ISS were being loaded with anti-virus software.

"All A31p laptops onboard are currently being loaded with [the] latest [Norton AntiVirus] software and updated definition files for increased protection," said NASA.

W32.Gammima.AG, the name Symantec Corp., maker of Norton AntiVirus, gives the malware, is a year-old Windows worm designed to steal information from players of 10 different online games, some of them specific to the Chinese market. Among the games: ZhengTu, HuangYi Online and Rohan.

The worm also plants a rootkit on the infected system, and transmits hijacked data to a remote server.

Today, Humphries said that the worm poses no threat. "It was never a threat to any command-and-control or operations computer," he said. He refused to detail how the malware snuck aboard, citing "IT security issues," but other sources, including SpaceRef.com, speculated that it might have stowed away on a laptop or a flash card.

In fact, the Aug. 11 ISS log entry hinted at digital camera storage cards as a suspect.

"There have been other incidents," confirmed Humphries, who works at the Johnson Space Center in Houston, Tex. "I don't know when the first one was, but the station will have been in orbit for 10 years [come] November."

"If there is any good news at all, it's that the malware was designed to steal usernames and passwords from computer game players, not something that orbiting astronauts are likely to be spending a lot of time doing," said Graham Cluley, a senior technology consultant with Sophos Plc., in a post to that company's blog today. "After all, with a view like that who needs to play the likes of World of Warcraft?"