[Coda]

No virus scanner is perfect -- new viruses will come out and they won't get detected by anyone for a couple days. That's why it's important to keep your definitions up to date. But my point is that you should never back up an .exe file or a .dll file if it's something you can reinstall from a CD/DVD or redownload from the Internet, because they could get infected. Non-program files are much less infectable.