It can target unlocked machine via USB in a matter of seconds. It does this by emulating a keyboard and mouse, blindly typing controlled commands, flailing the mouse pointer around and weaponizing mouse clicks.
Nearly every computer including desktops, laptops, tablets and smartphones take input from Humans via Keyboards. It's why there's a specification with the ubiquitous USB standard known as HID - or Human Interface Device. Simply put, any USB device claiming to be a Keyboard HID will be automatically detected and accepted by most modern operating systems. Whether it be a Windows, Mac, Linux or Android device the Keyboard is King.
By taking advantage of this inherent trust with scripted keystrokes at speeds beyond 1000 words per minute traditional countermeasures can be bypassed by this tireless trooper - the USB Attack.