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.

Those who have wrestled unhappily with the software's predecessor, Microsoft Live OneCare, will be pleased to know that Security Essentials suffers from none of the software bloat and slow performance that bedeviled OneCare. Unlike OneCare, Security Essentials doesn't do performance tune-ups, back up your PC, take up too much system resources - or cost a penny.

Installation and setup

Security Essentials comes in versions for Windows XP and Windows Vista (the Vista version will also work with Windows 7). Both are light downloads: The 32-bit Vista download weighs in at 4.8 MB, the 64-bit Vista version at 3.8MB and the XP version (there's only a 32-bit version) comes in at 7.6 MB.

Installation of the 32-bit Vista version on our machine took less than five minutes and was about as simple as an installation can be. There is one caveat, though: You need to have a validated copy of Windows. Not surprisingly, Microsoft's software won't work with pirated or non-validated versions.

Once installation is complete, the application downloads the latest anti-malware definitions. It then launches a quick system scan that took under ten minutes on my system.

Security Essentials uses a new feature called the Dynamic Signature Service, which employs a variety of techniques to check for malware even before that malware's specific signature has been identified. Microsoft says Security Essentials emulates the behaviour of programs before they run, and uses the signature created during the process to look for any suspicious behaviour or patterns of suspicious behaviour, such as starting an unexpected network connection or trying to modify certain protected sections of Windows. The Dynamic Signature Service then determines what action to take against the potential malware.

Once the software has scanned your system, you don't need to do anything else, unless it finds malware that it wants to kill or quarantine. New anti-malware signatures are automatically downloaded daily, using the Windows Update engine; you can also have the software to check for the latest definitions manually. Security Essentials also provides real-time protection, so it watches your system as you use it and warns you if you're downloading malware or if your system has been infected. The software also scans your system once a week by default. You can manually override the defaults and set up specific days and times to perform the scans; more about this later.