This is a cheap air drone that's got a computer on board, allowing it to search for unprotected Wi-Fi networks and hack into them from above, putting them under someone else's control without ever touching the ground.
The SkyNET drone is a $300 Parrot quadcopter with a Linux computer, 3G card, GPS unit and two Wi-Fi cards on board. When someone is controlling it using 3G, it can scoot around an urban area scanning for networks, automatically trying to break into any it finds. Once it finds computers that can be hacked, the pilot can take control and let them send out commands and attacks from there, with no way to trace it back to the hacker. The total cost of this thing is $600, which is pretty damned cheap for a flying hacking machine.
So next time you see one of these hovering outside your window, feel free to take a broom to it.