Avast Antivirus Home Edition, developed in the Czech Republic, offers capable malware detection and faster-than-average scan speed, both of which helped propel the app to the number two spot in our rankings of free antivirus software. Its clunky interface badly needs updating, however.

In AV-Test.org malware-detection tests, the program blocked a respectable 98.2 percent of samples out of a malware "zoo" consisting of about a half-million files. That wasn't enough for Avast to top the best performers, Avira AntiVir Personal and the unranked Panda Cloud Antivirus, but it's still a good showing. Avast didn't do quite as well in proactive-detection tests, which simulate how well a program would fare against new and unknown malware: Its catch rates of 46.1 percent (two-week-old signatures) and 41 percent (four-week-old signatures) put it in fourth place.

The app was relatively nimble at on-demand scans (which you start manually) and on-access scans (which occur automatically when you save or use a file), placing second in each test (behind Avira in both cases). It issued just one false positive (labeling harmless software as malicious).

In disinfection, Avast nearly matched the top performers (Avira and Microsoft Security Essentials), detecting and disabling 90 percent of the rootkits used in our tests. All three apps, however, also left behind Registry entries and failed to reverse all of the changes that the malware had made.

While Avast does well as a malware blocker and remover, it fares poorly as a program that people have to interact with. Its outdated interface has sections that look entirely different depending on whether you're running a scan, checking status, or changing settings. The scanning interface mimics a music player, but you probably won't be singing its praises. Be sure to read the how-to guide that pops up the first time you use the program, unless you enjoy scratching your head and growling at your monitor.

The Avast product is the only free antivirus software in our test group that requires you to register within 60 days to receive a free license key. It's also the only app that scans Web traffic for malware (AVG 8.5 Free's LinkScanner scans Web traffic for the attacks that can presage malware, but not for the malware itself), and it scans e-mail traffic as well.

Avast Antivirus will do a decent job protecting a PC from malware, but if you're willing to put up with a less-than-perfect interface (and some ads), you're better off going with Avira's top-notch blocking.