Closed system or not, it had to have been exposed to the outside world to get this infection in the first place.
RTFA.
Oh look, snark. How original.
I did read the article. If it's a closed system, it doesn't get a virus. The virus has to come from somewhere outside, and someone is responsible for exposing it. Maybe I have more experience reading between the lines of military-spec canned bull**** but they basically admitted as much.
I literally JUST posted how they plugged external drives into the machines in order to transfer maps across. So, had you read the article in its entirety, or just read my previous post, you would have seen that staring you in the face. So yes, snark, and well-deserved snark too.
The keylogger came from an external hard drive plugged into the closed-system in order to transfer maps. This is neither surprising nor particularly frightening... well, except that they don't scan external drives moving around the department, but the drone systems themselves appear to have been just fine. The fact that a computer somewhere in the military got a malware infection isn't in the slightest bit surprising either - plenty of systems with low-clearance requirements and fairly open access in government, and security on those systems will be by the lowest bidder. And if one of those was used to put the maps on the external drives in the first place, there's your source.
This isn't like someone hacked a top-secret military network, guys. This literally could have happened because a frickin' secretary brought pictures of her kids into work on a thumb drive.