Microsoft Security Essentials

Microsoft Security Essentials
http://www.microsoft.com/Security_Essentials/ 

A new free Antivirus to rival the likes of Avast!, Avira and AVG (huh, a lot of 'A' packages, eh?)...or so we hope. Microsoft has retired it's Live OneCare product in favor of their new Microsoft Security Essentials package.  So far, initial reviews have been favorable

Microsoft Security Essentials provides real-time protection for your home PC that guards against viruses, spyware, and other malicious software.

Microsoft Security Essentials is a free* download from Microsoft that is simple to install, easy to use, and always kept up to date so you can be assured your PC is protected by the latest technology. It’s easy to tell if your PC is secure — when you’re green, you’re good. It’s that simple.

Microsoft Security Essentials runs quietly and efficiently in the background so that you are free to use your Windows-based PC the way you want—without interruptions or long computer wait times.

In its first week, it has been downloaded over 1.5 million times...not bad, but it will be interesting to see how it performs in the long-term. 

I've installed it my pc in lieu of Avira and Avast!.  I usually go for Avira when configuring my personal customer's machines...no registration key to enter once per year, but this might be a good alternative due to its pure simplicity.

Client download is small, I've noticed no system slowdown and it even picked up a virus that Avira missed (but this might be because I did not perform a full scan with Avira before loading MSE).

One word of warning, though: If your Windows version isn't valid (i.e. it fails the WGA test), then it will not install.

Have you tried it?  What do you think?