Using a more powerful signal than the one that is being transmitted by satellites orbiting the Earth, the device tricks the drone into thinking it's someplace other than where it actually is. In effect, such a system can hijack a drone.
The spoofed drone used an unencrypted GPS signal, which is normally used by civilian planes. That means that given the right equipment, a terrorist could, in fact, hijack a drone just as the 9/11 terrorists hijacked U.S. commercial airliners, and turn them into missiles.
The difference is, these drones are pretty small, and won't do anywhere near the damage of a commercial airliner. Still, the threat is there. Humphreys said, "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.”
Naturally, one would think it would be more difficult to hack into a military drone, but Noel Sharkey, co-founder of the International Committee for Robot Arms Control still says it's not that difficult.
"It's easy to spoof an unencrypted drone. Anybody technically skilled could do this - it would cost them some £700 (about $1,100)for the equipment and that's it. [...]
Did Iran already manage to do that? Not only has the country claimed that it used GPS spoofing to bring down a U.S. drone - an RQ-170 Sentinel that American authorities confirmed has been captured - it has also claims to have been able to extract much useful information from it.