ClamWin Free Antivirus stands apart from other free antivirus software because it's open-source, with no proprietary or commercial aspects. But in the essential task of blocking malware, it doesn't get the job done.

ClamWin doesn't provide real-time protection, and it won't check files as you open them or have them written to your hard drive; its scans are on-demand only, which means they kick off when you schedule them or specifically tell the program to run one.

If its scans were effective, ClamWin might have been a worthwhile pick as an extra security layer to catch files that your regular antivirus utility might have missed. Unfortunately, It missed almost half of the Trojan horses, password stealers, and other baddies in AV-Test.org's zoo of malware samples, an ignominious performance matched only by PC Tools Antivirus. Against malware made to steal online-banking passwords, it was nearly impotent, missing more than two-thirds of such samples. In proactive tests meant to find how well a program can detect new malware, it did better, nabbing roughly one-third of the samples while using two-week-old signature files (top performer Avira AntiVir Personal caught just over half). But that still wasn't a satisfactory result by any means.

Its six false positives were more than the amount from any other free antivirus software save for Comodo Internet Security (which had an astonishing 62). It was the second-slowest app in on-demand scanning--only PC Tools Antivirus had slower scan times--and it put up the worst numbers for disinfection, detecting only six out of ten infections and cleaning only five. In a rare shining performance, it identified all ten active rootkits (stealth malware designed to hide other infections). In contrast, however, it did the worst job of removing those rootkits, cleaning up just four.

The app's basic interface lists your hard drives and allows for scheduling regular scans, but you'll need to schedule a separate scan for each drive. ClamWin also adds a right-click Explorer option to scan a specific file, but such scans are notably slow, and by default it only reports discovered malware; to get an option to clean it, you must change the settings to quarantine or delete the file.

Although running an extra on-demand scan can be good as backup for your regular antivirus application, ClamWin's poor detection rate means that you are better off running an online scan from a commercial software maker, such as BitDefender or F-Secure, and avoiding this open-source project.