The USB Killer is a booby-trapped, hand-made USB drive that will "burn down" your laptop if you insert it into your USB slot.
First described on the Russian site Habrahahbr, the USB Killer's origin story has now been translated into English:
The basic idea of the USB drive is quite simple. When we connect it up to the USB port, an inverting DC/DC converter runs and charges capacitors to -110V. When the voltage is reached, the DC/DC is switched off. At the same time, the filed transistor opens. It is used to apply the -110V to signal lines of the USB interface. When the voltage on capacitors increases to -7V, the transistor closes and the DC/DC starts. The loop runs till everything possible is broken down. Those familiar with the electronics have already guessed why we use negative voltage here. I'll explain to others that negative voltage is easier to commutate, as we need the N-channel field resistor, which, unlike the P-channel one, can have larger current for the same dimensions.
I'm not going to talk to you about the application area, but a former colleague says that it's like an atomic bomb: cool to have, but can not be applied.
USB Killer [Dark Purple/Kukuruku]