Microsoft today lifted the curtain on its Microsoft Security Essentials, the free successor to its OneCare security program.

MSE uses the same antivirus engine as the phased-out OneCare, but the new free program focuses only on malware blocking. It doesn't include a firewall, system optimizer or other security suite-type features.

When I reviewed a beta version of Security Essentials back in July alongside other free antivirus programs, MSE did a good, but not top-notch job at detecting Trojans, keyloggers and other malware, with a 97.8 percent overall block rate as tested by AVTest.org. It did shine in proactive tests that simulate how well an antivirus program can detect new malware that doesn't yet have a signature, and its performance there was topped only by Avira's AntiVir Personal.

The strong proactive performance may be thanks to its Dynamic Signature Service feature that checks new, potentially suspicious files against the latest available data on Microsoft servers . But its pokey scan speed held it back in our free AV software rankings - it was the slowest scanner we tested. For a full list of the MSE beta's performance results, see its lab test report.

Today's MSE, now available for download, doesn't add any new features or look any different from the beta version I reviewed, according to a Microsoft spokesman. The final version only includes some "code quality improvements, bug fixes, etc." when compared with that beta.

That beta looked good and was easy to use. If Microsoft has managed to ramp up Security Essential's scan speed, and ideally bump up its detection rate just a tad, since I checked out the beta, then it will likely be a good choice for budget-conscious protection. Tech-savvy users willing to put up with an at-times annoying interface, as well as a daily pop-up ad, might prefer the stronger malware detection rate in Avira AntiVir Personal, which took top billing in the free AV ratings.

If you do decide to use MSE, be sure you enable the built-in Windows firewall or use a third-party alternative. You might want to pair Security Essentials (or any other free AV app) with the also-free PC Tools Threatfire, which adds an effective additional layer of behavioral detection that can catch new, unknown malware.