Microsoft's just-released free AV software has already been put to the test, literally: In an early test by an indie laboratory, the much-anticipated Microsoft Security Essentials (MSE) detected and removed all rootkits.

AV-Test.org reports that MSE found and killed all 25 rootkits tossed its way during a test it conducted on the new software, which Microsoft rolled out on Tuesday. MSE basically replaces Microsoft's subscription-based OneCare product, but focuses solely on anti-malware -- detecting and removing viruses, spyware, rootkits, and Trojans. It doesn't come with security "suite" functions, like a firewall, computer maintenance tasks, or backup.

AV-Test.org tested the new version 1.0.1611.0 with virus and spyware definitions 1.67.178.0 on Windows XP SP3, Vista SP2, and Windows 7.

Rootkits traditionally have been the nemesis of many AV products. But Andreas Marx, CEO of AV-Test.org, says MSE's 100 percent rootkit detection rate was "very impressive."

MSE also detected all 3,700 samples of static malware, but the software was unable to detect new, unknown malware using dynamic, behavior-based detection. "None of the samples were detected based on their suspicious behavior," Marx says. But, he says, other AV-only packages don't include this dynamic detection feature, either. It's usually only available in Internet security "suite" versions of the products, he says.

On XP, MSE found 98.44 percent of current samples of viruses, worms, Trojans, and bots, and 90.95 percent of adware and spyware.

AV-Test.org found that MSE was able to remove all active malware components during the repair and cleanup phase, but in some cases residual pieces from the infections remained, such as inactive executable files and a disabled Windows firewall.

"The scan speed is quite OK when compared with other AV products. The scanner is not the fastest one, but also not the slowest available," Marx says. He notes the test was a quick summary of some of the product's features, and that the lab plans to conduct more in-depth testing and reviews of MSE.

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