Microsoft's Security Essentials is officially available from today, offering free protection against malware for any PC user with a valid copy of Windows from XP Service Pack 2 onwards. The suite is primarily aimed at consumers, but the fact that it is free could also prove attractive to smaller businesses.

Available as a free download from 5pm UK time today, Microsoft Security Essentials supersedes the Windows Live OneCare subscription service that was discontinued earlier this year, and provides protection against viruses, spyware and other malicious software.

Microsoft claims that Security Essentials will run better on older or low performance hardware than other security tools, but rival vendors have stated that Microsoft's product is simply not as effective as paid-for solutions.

Microsoft said that it decided to introduce a free security product because the number of malware attacks is growing, yet many users still do not have any protection against threats.

"About 50 per cent of PC users in the UK do not have up-to-date anti-virus software, and it doesn't make business sense for Microsoft if lots of Windows PCs are getting infected," said Julia Owen, Windows Client product manager for Microsoft UK.

As well as cost, Owen believes that performance is another major barrier to users properly protecting their computers.

"People find that the security suites adversely affect the performance of their PC, especially low-power systems like netbooks," she said.

In contrast to other tools, Security Essentials requires a minimum of just 256MB memory and a 500MHz processor on an XP system, and 1GB memory and a 1GHz processor for Vista or Windows 7, according to Microsoft.

"We wanted it to be capable of running on as many machines as possible, and it runs quietly and silently. You just install it and forget it," said Cliff Evans, head of security and privacy for Microsoft UK.

Because the system protects against threats including viruses and spyware, it also replaces Windows Defender, Evans said, deactivating it on installation.

Evans added that Security Essentials is a high-quality anti-malware product based on the same technology as Microsoft's Forefront security products for business, and claimed that it "compares favourably" with commercial security suites.

The software has achieved good results in independent tests from organisations such as AV Comparatives and West Coast Labs, he said.

However, rival vendors such as Symantec have cast doubts on the effectiveness of Microsoft's free product.

"Microsoft Security Essentials is a stripped down version of their old OneCare product which was poorly rated by industry experts and users alike," a Symantec spokesperson told V3.co.uk.

"From a security perspective, this Microsoft tool offers reduced defences at a critical point in the battle against cyber crime."

Symantec claimed that its Quorum reputation-based technology can identify entirely new spyware, viruses and worms without relying on signatures.