Houston, We Have Virus Lift-Off
A lesson for us all? Yep.
However, the virus wasn't something that would bring the ISS crashing to Earth. The W32.Gammima.AG worm is pretty old: discovered last August. Since it targets passwords to various online games, and the lag from the ISS would be pretty bad, it's safe to say that the astronauts weren't doing anything that the virus would find inviting.
NASA believes the virus may have infected the laptops via a flash drive one of the astronauts used. This certainly makes sense, as the virus propagates by using removable media, according to Symantec.