Microsoft's new free antivirus product - Microsoft Security Essentials - is now available in beta.

While UK web users who visit this Microsoft Security Essentials website are greeted with the message "Not available in your country or region", the software is available to UK users of Microsoft's Connect service.

Microsoft is pitching Security Essentials as a basic antivirus, antispyware product that consumes less memory and disk space than commercial security suites from vendors such as Symantec and McAfee, and so is suitable for even low-powered computers such as netbooks.

"Netbooks are one focus of Windows Security Essentials," said Alan Packer, the general manager of Microsoft's anti-malware team. "We have tested it on netbooks, and a gigabyte [of memory] is actually plenty."

However, he conceded that on systems with slower processors and limited RAM, the software will hit performance, especially when users run multiple applications at the same time.

"I don't want to oversell here," Packer said. "There's definitely an impact on netbooks, and although we're trying to minimise [that], you're going to notice it's there."

Security Essentials runs on Windows XP, Vista, or Windows 7 (beta or release candidate), and first impressions indicate it does pretty much what any good anti-malware app should do. It automatically downloads virus and spyware definitions; offers real-time protection that scans downloads and attachments, and looks for suspicious file and program activity; and runs unattended scans at a time that works best for you.

See our Windows Security Essentials review.

PC security advice