Earlier this month, cosmonauts on the International Space Station discovered a computer worm that had hitched a ride from Earth on a laptop.

The bug turned out to be benign, but the fact that it got on board has raised concerns about the space station's vulnerability to such digital intruders. New Scientist takes a closer look.

What is the virus?

NASA spokesman Kelly Humphries declined to name the invader but described it as a "worm-like virus," a small piece of software that copies itself to spread from computer to computer - via the internet or shared media such as flash drives.

But Keith Cowing, who broke the story on the website SpaceRef on Monday, reports that the culprit is a virus called W32.Gammima.AG. The information came from a recent review of the space station's operations.

According to Symantec - maker of the popular Norton antivirus software - the Gammima worm's only purpose is to steal usernames and passwords from 10 online games popular in China. It can travel on removable media like flash drives and is classified as a low threat that is easy to remove.

Indeed, Humphries says the worm posed no risk to the command and control systems of the ISS, though he declined to give specifics, citing security concerns. "It's a nuisance... that hasn't affected the operations of the space station," Humphries told New Scientist.

How did it get aboard?

The International Space Station is a joint project of 15 countries, including the US, Canada, Russia and Japan. Each partner, says Humphries, maintains its own computer equipment according to a set of agreed-upon rules. This worm infected a Russian laptop used to run scientific experiments.

Viruses can be hard to catch because new ones are constantly appearing, says Jose Nazario of Arbor Networks Security in Ann Arbor, Michigan. A study by Microsoft found that nearly 43,000 new pieces of software appeared in the first half of 2006 alone. Nazario's own research has shown that popular antivirus software packages can miss or misidentify 20 to 49% of these viruses.

"NASA weighs anything that goes up and assesses it for toxicity, but for software this is harder to do," says Paul Ceruzzi of the National Air and Space Museum in Washington, DC.

What is NASA doing to get rid of the virus?

Last Friday, 22 August, Commander Sergei Volkov updated the files of the Norton antivirus (NAV) software installed on the laptop.

"All A31p laptops onboard are currently being loaded with latest NAV software and updated definition files for increased protection," reads the ISS daily log. The three crew members aboard the space station manage over 50 computers.

Should we be worried?

Humphries says that though this is not the first time a virus has been found on the ISS, such incidences are "not a common occurrence".

In a worst-case scenario, according to Nazario, a virus or worm could have serious implications for the scientific experiments conducted on the station.

The laptops communicate with each other on a local area network (LAN) in the station - similar to that found in an office. A worm could clog up this connection as it tries to propagate itself.

Even worse, some worms can hide in commercial software packages and delete data on the hard drive. Says Nazario: "Remember the term paper that got chewed up in college? Imagine a million-dollar experiment down the toilet."

What problems might come up in the future?

The laptops used on the space station have no direct connection to the internet; the crew members cannot browse the web.

The email they received is managed in accounts on the ground, where all messages are scanned for viruses before they are sent up to the space station via a KU band connection, similar to that used by TV stations to communicate with satellites.

But the integration of internet-age technology may be starting to present new challenges for the space programme. "This worm was a wake-up call," says Ceruzzi.

Courtesy Computer Crime