MalDuinos are BadUSBs. They appear to a target computer as a keyboard, this allows them to type out text at lightning speed. Why is this useful?
You can complete almost any task on a computer just with keyboard input, opening a command prompt in admin mode is only a few keys away. Keyboard input is inherently trusted by computers, meaning there is no barrier to entry other than a USB port. Writing a BadUSB script is easy, there are also thousands of compatible scripts available freely online.