From Bobak I saw that US drones in Iraq have been hacked because “the remotely flown planes have an unprotected communications link” but “there was no evidence that they [insurgents] were able to jam electronic signals from the aircraft.”

This illustrates nicely the difference between eavesdropping and jamming. However, a nice by-product of anti-jamming codes using shared encryption keys (here they can be easily agreed upon before the drone takes off) is that sometimes you can get both eavesdropping and jamming protection at the same time.