You’ve got one less excuse for leaving your computer unprotected against viruses and spyware: Microsoft recently added its new software package, Security Essentials, to the list of free antivirus tools available for download online.

We gave Security Essentials a preliminary test run on several PCs here in our labs. The program installed in less than a minute on the typical PCs we tried, appears to use relatively few system resources, and has reasonable default settings. It’s compatible with Windows XP or later.

The user interface is deceptively simple, which is a good thing. The program automatically updates itself, and performs a quick scan every Sunday night by default, though you can change that and other settings.

If you have antivirus software already, there's no need to change. If you decide to make the switch to Security Essentials, be sure to uninstall your old antivirus program first. Security Essentials disables Windows Defender if it finds it, since they duplicate anti-spyware tasks, and since running two real-time anti-spyware programs can lead to problems.