Robert Slade, author and computer virus expert, explains what viruses are and how to beat them:
A virus is any program that reproduces itself by using the resources of your computer without your knowledge or consent. Most are not intentionally malicious. A truly malicious virus -- say, one that erases an entire hard drive -- doesn't have much chance to spread because it destroys its "host." But any virus you get will eventually conflict with something on your system. People think that viruses have something to do with pirated software and that if they don't have a modem, they're safe. And everyone thinks, "it can't happen to me." None of those three things is true.
First of all, back up regularly. Second, everybody should have antiviral software; there's no excuse not to get it. I think shareware is often better than the commercial products. Many antiviral software vendors have introduced Windows 95, LAN, and Internet versions of their software, but they cannot guarantee protection. You should check each file attachment or Web-based installation you receive. Check every disk and new program you receive. Some antiviral software can monitor your system automatically, either all the time or at regular intervals. And finally, keep your antiviral software up-to-date.
You can remove most viruses by running good antiviral scanning software. If you can't fix the problem easily, confirm the virus with a second brand of software -- it is possible to get a "false positive." If necessary, delete the infected file and reinstall it from your backup. Then scan all disks with the antiviral software, or you may reinfect your computer.