Researchers say with the right equipment, anyone can take control of a GPS-guided drone and make it do anything they want it to. GPS “spoofing” could cause a drone to veer off its course and even purposely crash. This is particularly worrisome given that the US is looking to grant US airspace to drones for domestic jobs including police surveillance or even FedEx deliveries. Congress recently passed legislation paving the way for what the FAA predicts will be somewhere in the region of 30,000 drones in operation in the US skies by 2020.
Source: https://thehackernews.com/2012/06/drones-can-be-hijacked-by-terrorist.html