I'd suggest the current Norton Anti-virus. No, it's not free, but free updates are available and this allows you to keep up-to-date on virus definitions. A virus routine that "will block or close down any program that tries to alter your computer files" will simply not work, e.g. files are routinely altered for many, many applications: this is what makes your computer do what it does. I've used Thunderbyte, a freeware virus program that's not bad, but I'd really suggest biting the bullet and buying youself a copy of the current Norton Anti-virus. Then about once a week, check into Norton's website for updates. And if you're running Windows 9X, hit the Microsoft website now and then for updates. Windows 9X, particularly its e-mail functions, are often vulnerable to intrustions and the Microsoft website has updates now and then that close some of these security holes. Don't hesitate to e-mail me if you have questions or want to chat about computer security; I'll be glad to help you out if I can. And no, I'm not employed by Norton or Symantec.