The control of US military spy drones appears to have shifted from Windows to Linux following an embarrassing malware infection.

Ground control systems at Creech Air Force Base in Nevada, which commands the killer unmanned aircraft, became infected with a virus last September. In a statement at the time the Air Force dismissed the electronic nasty as a nuisance and said it posed no threat to the operation of Reaper drones, but the intrusion was nonetheless treated seriously.

"The ground system is separate from the flight control system Air Force pilots use to fly the aircraft remotely; the ability of the pilots to safely fly these aircraft remained secure throughout the incident," it said.

The discovery of the virus was nonetheless hugely embarrassing for the Air Force. The credential-stealing malware, first reported by Wired, made its way from a portable hard drive onto ground systems, which control the drones' weapons and surveillance functions. Portable disks are used to load map updates and transfer mission videos from one computer to another, Defense News added.

"The malware was detected on a standalone mission support network using a Windows-based operating system," a US Air Force statement at the time explained. "The malware in question is a credential stealer, not a keylogger, found routinely on computer networks and is considered more of a nuisance than an operational threat. It is not designed to transmit data or video, nor is it designed to corrupt data, files or programs on the infected computer. Our tools and processes detect this type of malware as soon as it appears on the system, preventing further reach."

Drone units were advised to stop using the removable drives to prevent another outbreak. Behind the scenes other changes appear to have been made: screenshots of drone control computers uploaded by security researcher Mikko Hypponen suggest that at least some of the consoles have been migrated from Microsoft Windows to open source Linux.

Photos of US drone control systems taken in 2009 (here) and 2011 (here) provide evidence of the change - in the earlier picture the Windows desktop GUI can be easily discerned whereas the latter slide indicates the new systems are Linux-based and have "improved displays".

The 2009 photo originally came from the air force base's website but the image has since been removed. A cropped copy can be found here. The 2010 slide came from an unclassified presentation on the US's unmanned drone operations.

Hypponen told The Reg: "If I would need to select between Windows XP and a Linux based system while building a military system, I wouldn't doubt a second which one I would take." ®