If an attacker can convince you to plug his USB device (like an iPod) into your computer, he can take it over.
Plug an iPod or USB stick into a PC running Windows and the device can literally take over the machine and search for confidential documents, copy them back to the iPod or USB’s internal storage, and hide them as “deleted” files. Alternatively, the device can simply plant spyware, or even compromise the operating system.\