The default configuration of udev on Linux does not warn the user before enabling additional Human Interface Device (HID) functionality over USB, which allows user-assisted attackers to execute arbitrary programs via crafted USB data, as demonstrated by keyboard and mouse data sent by malware on a smartphone that the user connected to the computer.
http://www.blackhat.com/html/bh-dc-11/bh-dc-11-briefings.html#Stavrou