Earlier this month, it became known that the US Air Force's aerial drones had been infected with malware. It didn't blow them up or anything, but it was embarrassing for the Air Force nonetheless.
It's even more embarrassing now.
According to an "anonymous defense official" speaking with the Associated Press, via Wired, the type of malware plaguing the aircraft and logging their user's keystrokes is the kind "routinely used to steal log-in and password data from people who gamble or play games like Mafia Wars online."
So the crews were either using computers at work to play social games/gamble, or were sticking thumb drives into military computers that had been around people playing social games or gambling. A perfectly feasible explanation!