Security Essentials runs on Windows XP, Vista, or Windows 7 (beta or release candidate), 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 rootkit 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.)

During a Security Essentials system scan, Microsoft Word 2007 took 14 seconds to load, 3 seconds longer than normal.

Of course, a security app's true value is determined by its malware-fighting skills, and PC World will post a detailed review of Microsoft Security Essentials in the near future. How will this free app fare? There's reason for optimism here, as Redmond has received accolades lately from the same experts who trashed its previous security efforts.

Go to jbertolucci.blogspot.com for links to Jeff Bertolucci's PC World blog posts.