You might want to research 'disabling autorun' in Windows.
I believe default Windows behaviour is to look for an autorun file on any drive which is plugged into the USB. Executing the autorun is most likely when the virus installs itself, perhaps before your virus scanner even has a chance to scan the files on the disk.
Yes, you will then have to search for the files on the disk using windows explorer as the pop-up window will likely cease to pop up when autorun is disabled. Not a big deal for a bit of security.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)