Iran hacked US drone?

"By putting noise [jamming] on the communications, you force the bird into autopilot. This is where the bird loses its brain."

The team then use a technique known as "spoofing" -- sending a false signal for the purposes of obfuscation or other gain.  In this case the signal in questions was the GPS feed, which the drone commonly acquires from several satellites.  By spoofing the GPS feed, Iranian officials were able to convince it that it was in Afghanistan, close to its home base.  At that point the drone's autopilot functionality kicked in and triggered the landing.  But rather than landing at a U.S. military base, the drone victim instead found itself captured at an Iranian military landing zone.

Spoofing the GPS is a clever method, as it allows hackers to "land on its own where we wanted it to, without having to crack the [encrypted] remote-control signals and communications." 

DailyTech:
Iran: Yes, We Hacked the U.S.'s Drone, and Here's How We Did It