The just-released beta of Microsoft Security Essentials - not yet available in the UK - is a solid, free tool that protects against malware while taking up few system resources and staying out of your way as much as possible.

Microsoft Security Essentials shows much promise. In our tests it was decent at detecting malware, particularly in proactive tests that simulate the handling of new, unknown malware. It took fourth place in our rankings of free antivirus software. The main drawback of the tool, due to launch on September 29, seemed to be its slow scan speed.

One thing we hope Microsoft will improve is Microsoft Security Essentials' relatively poky scan speed. It was the slowest in our on-access scan test, which judges how quickly scans run when you copy, open, or save files. The app's Dynamic Signature Service may account for some of that: When Security Essentials sees a potentially malicious file that doesn't match known malware, it contacts Microsoft servers for additional analysis. The feature likely affords greater protection owing to the use of the latest signatures online, but it may also introduce some delay if Security Essentials has to wait for a response.

Microsoft Security Essentials' ability to detect and block malware was neither especially good nor particularly bad. Its 97.8 percent overall detection rate put it in fourth; but it did well in proactive tests, which use two- and four-week-old signature databases to simulate how well a program detects new, unknown malware. Its results of 52 percent and 43.8 percent, respectively, were second only to those of the top-ranked Avira Antivir Personal, our overall winner.

Microsoft Security Essentials put up no false positives (flagging of benign software), and it got a near-perfect score overall in detecting and cleaning rootkits and malware infections. It detected and disabled every infection, and although it left behind several changes to the Registry and other areas (as every free app did), they couldn't cause further harm.

The just-released beta of Microsoft Security Essentials - not yet available in the UK - is a solid, free tool that protects against malware while taking up few system resources and staying out of your way as much as possible.

This is set-it-and-forget-it software that handles the basic dangers, but doesn't try to compete with big-boy security suites such as those built by Symantec, McAfee or Panda. So you won't find extras such as a firewall, identity protection, anti-phishing technology or anti-spam. Instead, Security Essentials focuses on protecting you against viruses, spyware, rootkits and similar dangers, and does a very good job of it.

Check out more business and security reviews