A group of researchers at the University of Texas at Austin’s Radionavigation Lab made a phone call to the Department of Homeland security this week. The lab team, led by Todd Humphreys, wanted to show DHS how they were able to take control, or “spoof,” a drone plane by hacking its GPS. Until recently, the biggest concern for drones has been a hack called “jamming,” where the GPS info gets scrambled. It’s believed that jamming was the cause of a recently downed drone in Iran.
Spoofing is a whole new ballgame, however. Fox news has the story:

[S]poofers are a giant leap forward in technology; they can actually manipulate navigation computers with false information that looks real. With his device — what Humphreys calls the most advanced spoofer ever built (at a cost of just $1,000) — he infiltrates the GPS system of the drone with a signal more powerful than the one coming down from the satellites orbiting high above the earth.

The signals that Humphreys and his group were spoofing are all unencrypted, but the same techniques can be applied to encrypted signals used by the military. Humphreys called attention to non-military drones that might soon fill the sky over the U.S.
“What if you could take down one of these drones delivering FedEx packages and use that as your missile? That’s the same mentality the 9-11 attackers had,” Humphreys told Fox News.