Can you imagine finding a USB in the bathroom, and you plug it into your computer back at the office to find out who it belongs to — ZAP! Your computer screen flickers and then goes black. You try anything to turn it on or find a sign of life, but the device is fried due to the USB Killer.
The USB Killer takes advantage of the USB Power Surge vulnerability found with most devices. Most manufacturers save money by not protecting the power or data lines of devices, leaving the ports open for an attack.
The USB Killer rapidly sends high-voltage power surges into the device it is plugged into, damaging the hardware components. With -200VDC discharging multiple times per second, it destroys the motherboard almost immediately.
Originally, the USB Killer was developed to test these Power Surges to ensure that they are protected. The device is primarily used as an attack, as it is mentioned in articles warning readers against plugging in unknown USB Drives.