Usbdumper - http://www.schneier.com/blog/archives/2006/08/usbdumper_1.html:
USBDumper is a cute little utility that silently copies the contents of an inserted USB drive onto the PC. The idea is that you install this piece of software on your computer, or on a public PC, and then you collect the files -- some of them personal and confidential -- from anyone who plugs their USB drive into that computer.
There is allready a nice little guide for creating a usb hawksaw using this Usbdumper program:
http://www.hak5.org/wiki/USB_Hacksaw
Would be nice if Avast could detect this