Here are my own three favourites for keeping a single home computer reasonably safe and clean:
1. F-Secure Anti-Virus and Firewall
http://www.f-secure.com/en_US/produc...rnet-security/
2. SuperAntiSpyware, both as preventive measures but also if you ever get anything, this is one of the few which can handle some really complicated shit.
http://www.superantispyware.com/
3. SpyBot Search & Destroy. Has an immunization feature, to immunize your system from new threats all the time. Also now has a boot-cd for those nasties which simply won't go away while running the system normally, now you can remove them before Windows is even loaded.
http://www.safer-networking.org/en/index.html
And also, the oldest trick in the book, but free and unforgivable if you don't:
4. Schedule a weekly download of Windows updates. Make sure to schedule it during a time when the computer is ON, many old people turn off their computer at night and the scheduler often comes pre-programmed to do its updates and installs at night, which means that it rarely or very seldom happens.
Microsoft still has their Tuesday updates, all updates which are not marked as emergency updates, are released on Tuesday mornings every week. So schedule the automatic updates to take place on Tuesday lunch, afternoon or evening. Make sure it's selected to e fully automatic, without any user interaction and setup and configured so for ALL users which might be logged in on the machine.