The SkyNET drone is a modified $300 Parrot quadcopter with a Linux computer, 3G card, a GPS unit and two Wi-Fi cards. This is how it works:
Controlled by a botmaster using 3G, the drone or group of drones fly over any urban area looking for Wi-FI networks. As they find them, they automatically try to break in. Once they get inside the network, it searches for personal computers that can be compromised. Any computer that falls to the attack gets turned into a zombie without the user ever knowing it.
Still not scared of robots?