747Focal - If man can make it man can break it - very very true.
Seriously though, with all the authentication protocols available today hijacking the control signal between a UAV and it's ground control would be very very difficult, if not dare I say this to Mr. Focal impossible? Frequency hopping, 128bit data encryption, message authentication etc etc.
What is perfectly possible is to block the signal, but if the aircraft is at cruising alt and speed you'd have to be following it in another aircraft to jam the signal for any meaningful amount of time. If that did happen then yes, software in the UAV would have to find some water and ditch in it. Then the Cessna float plane that was following it would land beside it, break into it and steal the knitting needles, parrot, used panties that it was transporting (refer to the strangest freight thread in Cargo).
