Security software is a necessary evil. Sometimes the problems it causes are almost as bad as what it’s supposedly protecting against. For example, in the process of preventing spyware from slowing down Windows, anti-spyware software tends to… slow down Windows.
You’re lucky if slowness is the only downside to running real-time protection. McAfee has managed to cripple thousands of Windows XP users with its latest security update, which mistakenly quarantines an essential system file:
http://news.cnet.com/8301-1009_3-20003074-83.html
This is what I do for Windows security at home:
That’s it. And none of them cost anything except the time and effort to set up. Oh, and something else. If you use a mail client like Outlook Express or Thunderbird, pre-screen your mail with a web browser and delete anything suspicious before downloading it.