BadUSB, a USB drive that turns into a keyboard

BadUSB is a hack announced at Black Hat USA in 2014, that is both ingenious and terrifying. A standard USB drive is re-programmed so that shortly after being plugged in, it changes its device type to a keyboard. From there, it can quickly enter keystrokes to install malware onto the host machine.

See the demo and full technical explanation in the video. The demo starts at the 1 minute mark.