Install and keep up-to-date a good antivirus program. AVG is free! It works well and automatically keeps itself up-to date. Not for Windows 98 or ME. Current version: 8.0 This has an anti-spyware component as well. (V7.5 users will have to update). Avast v 4.8 also works well and supports Windows 98 and Windows ME
Install a firewall program. Windows XP users get one provided by Microsoft as part of the Service Pack 2 (SP2) upgrade. Other users could use ZoneAlarm (also free). I find it works well.
Get on top of spyware/malware that sneaks into your PC. Windows XP users can use Microsoft Defender (for free!) and other users could run Spybot or Ad-Aware (both free) on a weekly basis.
Download Microsoft updates. I know it is a pain (especially for dial-up users) but I do believe they are trying to improve your PC's security.
Resist the urge to download "free programs" unless you have googled them to see if they are safe. Some of them introduce unwanted nasties of their own. You have been warned!
Ring me (Bryan Butler 06-3049931) or send me an email to firstname.lastname@example.org this all seems too much.