“Spoofing a GPS receiver on a UAV is just another way of hijacking a plane,” Humphreys told Fox News.
In other words, with the right equipment, anyone can take control of a GPS-guided drone and make it do anything they want it to.
“Spoofing” is a relatively new concern in the world of GPS navigation. Until now, the main problem has been GPS jammers, readily available over the Internet, which people use to, for example, hide illicit use of a GPS-tracked company van. It’s also believed Iran brought down that U.S. spy drone last December by jamming its GPS, forcing it into an automatic landing mode after it lost its bearings.
Read more: http://www.foxnews.com/scitech/2012/06/25/drones-vulnerable-to-terrorist-hijacking-researchers-say/#ixzz1zJEVGsaZ
The story focuses on UAVs, where the problem is an immediate concern. But the implications extend to civilian airliners, ships, trucks . . .
A footnote: The story says that the UAV was downed by this technique; that's a bit more definitive than any report I've seen.