ClamXav 1.1.’s killer feature is simple: price. The program doesn’t come out ahead if you compare its features, speed, or usability with commercial antivirus programs that cost a lot more, but it does a good job of finding viruses at an unbeatable price: free (donations requested).

ClamXav is a graphical front end for the open-source ClamAV antivirus engine, which is often found running on Unix e-mail systems. ClamAV is well known among open-source proponents, and more importantly, its virus definitions are updated daily. The interface offers a number of options, but for those new to the program, routine operations—such as making sure your Mac is being actively scanned and threats are being quarantined—can be a little confusing.

ClamXav detected all the viruses on my test Mac, and the program offered by default to delete the infected files. If you set up a special area on your disk called Quarantine, those files will be safely stored; however, ClamXav can’t repair infected files. It took just under 8.5 hours for the program to scan my entire hard drive (170GB of data). The other antivirus programs we tested—Norton AntiVirus 11 ( ) and VirusBarrier X5 ( )—scanned the same amount of data in less than half the time. Given that its scans take so long, it’s good that ClamXav doesn’t automatically scan volumes attached to your Mac, though you can enable that feature if you want.

While ClamXav scanned my Mac, I was able to use it normally; however, I did notice slowdowns as the program scanned larger files. The scanning didn’t make my Mac grind to a halt, but my computer was occasionally sluggish while switching and launching applications.

You can easily schedule scans and update virus definitions. Out of the box, ClamXav isn’t set up by default to check for updates. So it’s possible that ClamXav’s scans could miss newer threats due to outdated definitions. It would be nice if future updates prompted the user to set up an update check schedule upon installation.

An additional application that comes with ClamXav, called ClamXav Sentry, can be set to monitor folders in real time. ClamXav Sentry, which was completely rewritten for ClamXav 1.1, sits in your menu bar when activated and silently watches over the folders you point it to. Telling Sentry which folders to watch involves dragging the folders into the ClamXav Sentry window, which can be a little cumbersome if you’re trying to select several folders at the same time. When Sentry detects a virus, it pops up an alert that allows you to either put the virus in quarantine (assuming you’ve set up a quarantine folder), move the file to the trash, or ignore the alert. The application also supports Growl, the systemwide notification feature, which allows ClamXav and Sentry to alert you.

Macworld’s buying advice

ClamXav 1.1 is an able antivirus program that will keep your Mac protected, though it doesn’t offer all the features that more-expensive programs do. Free is hard to beat, though, and while ClamXav might be slower than other programs, and might slow down your Mac a bit, it’s just as accurate.

[Scott McNulty is a full-time geek living in Philadelphia. He is lead blogger at The Unofficial Apple Weblog and cohost of the cooking podcast, Fork You.]