In doing so, I believe my USB drive has picked up some malware. In Windows it appears on the desktop as a green icon with 'Keygen' written on it. It also creates a message box saying 'UpdateNetFramework'. If I delete the file it simply reappears. Symantec Norton Internet Security 2009 hasn't managed to eradicate it, and I now have the same message on all the USB drives I use. Dr Alok Modi
HELPROOM ANSWER Back up any files and folders you require, then wipe your hard drive and reinstall Windows. You need to remove the files without booting into Windows, however, since any drive you plug in will get infected.
First, buy a new USB drive with the capacity to store all your files. Using a different PC, download a copy of Ubuntu and burn the ISO file to a blank CD. Print out the instructions given here on how to recover your Windows files using a Ubuntu boot disc.
Insert the Ubuntu CD and plug in the new USB key. Restart your PC, but boot into Ubuntu on the CD rather than Windows.
This is important: should you boot into Windows at this point, your new USB drive will also get infected. Follow the instructions to transfer your files to the drive.
Having done all this, format your hard drive and reinstall Windows. Remember to reinstall your security software and any updates that are required.
See also: How to delete a file that just won't die