Here is a small free program that may come in handy. Its called Clamwin Portable. Available at Description from the website:

ClamWin Portable is the popular ClamWin antivirus packaged as a portable app, so you can take your antivirus with you to scan files on the go. You can place it on your USB flash drive, iPod, portable hard drive or a CD and use it on any computer, without leaving any personal information behind.
I have this app loaded on my USB key along with its virus definition database. I have used this app when a pc is infected with a virus that may prevent the installed Antivirus program from running or updating its own virus database.
I have used ClamWin Antivirus many times to fix pcs that have no internet access and cannot update their own virus software. I can update the virus database on the USB key from another pc and then connect the USB key to the infected pc.
I beleive this app can also be run from a CD although I have not used it that way. I imagine you would need to burn a new cd every time the virus database is updated.
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