Install the long-awaited Avast 5 and one change is immediately obvious: the old media player-style interface has been replaced by a clean, attractive grey-orange design. It looks more professional, and the new tabbed navigation also makes the program far easier to use.

You won't necessarily have to explore Avast 5's features right away, though, because an extensive range of real-time shields will automatically protect you from a wide range of threats. P2P and instant messaging traffic, network connections and browser downloads are all checked for malware. A new Behaviour shield looks for programs that are acting suspiciously, while other components keep a close watch on your file system, incoming and outgoing emails.

When you do start running system scans you'll find they include some useful changes, too. A new Intelligent Scanner builds a white list of proven safe applications, which then aren't scanned again unless they change, a feature that's claimed may reduce files scanned by up to 80%. Multi-threaded scanning optimisations split the scanning of large files between cores, again improving performance. And memory and system resource requirements are all lower than in previous versions.

Other benefits include a new gaming mode, which automatically detects full-screen applications and temporarily disables pop-ups and alerts. And a new format for the virus definition files means updates can be applied faster than ever, with reduced demands on your RAM and CPU.

Avast Free Antivirus doesn't include a firewall, spam filter, sandbox or malicious script detector - they're only to be found in the commercial Avast Pro and Avast Internet Security - but at this price we're not complaining: it's an excellent security tool.