So how did they send it GPS signals as Admin's link says? (I'm sure it was more complicated than said link describes)
You 'simply' broadcast your own false GPS signals from a ground station. GPS is a very weak signal, so it's not hard to drown it out. Mimicking it requires a lot of math, though . . .
Must have taken a bit of work though - like knowing at what precise location it was supposed to land.
Yea, I wondered that too. They probably tracked down the airport in a nearby country.
I'm thinking that a computer vision recognition system to visually identify the correct landing location might make a good defense . . . given the hardware on these spy drones, I'm sure it's just a small software update
On a side note, it's common for spy hardware to have anti-tamper and self-destruct features to prevent reverse engineering in case of capture. It appears that was not the case for these drones . . .