According to the International Business Times, Russian cosmonauts brought a removable device into the International Space Station, which infected the space station's systems.
Kaspersky doesn't give any details about when the infection he was told about took place, but it appears as if it was prior to May of this year when the United Space Alliance, the group which oversees the operaiton of the ISS, moved all systems entirely to Linux to make them more "stable and reliable."
Prior to this move the "dozens of laptops" used on board the space station had been using Windows XP, which is inherently more vulnerable to infection from malware than Linux.
According to Kaspersky the infections occurred on laptops used by scientists who used Windows as their main platform and carried USB sticks into space when visiting the ISS.
The ISS's control systems (known generally as SCADA systems) were already running various flavours of Linux prior to this switch for laptops last May.
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