Security Essentials runs on Windows XP, Vista, or Windows 7 (beta or ), and does pretty much what any good anti-malware app should do. It automatically downloads virus and spyware definitions; offers real-time protection that scans downloads and attachments, and looks for suspicious file and program activity; and runs unattended scans at a time that works best for you (e.g., Sunday morning at 7 a.m.).

The program's interface is clean, uncluttered, and non-threatening to users who don't know a from a root canal. A green icon shows you're protected. And a red-orange icon means trouble, such as if real-time protection is turned off.

While this sort of visual reporting is common among anti-malware apps, Microsoft's presentation is jargon-free and easy to follow.

Security Essentials' Settings tab provides fast access to advanced tools that power users might reconfigure. Example: The ability to scan removable devices such as USB flash drives, a feature that's turned off by default. You can schedule scan times too.

I just downloaded Security Essentials this morning and installed it on a creaky Toshiba laptop running Windows XP. So far I haven't witnessed a big drag on system performance, a problem I've encountered over the years with bloated security suites from Norton and McAfee. (My Toshiba note has 512MB of memory; Security Essential's minimum RAM requirement for XP is 256MB.)