Though Alwil Avast Professional Edition ($40 for a one-year, single-PC license, as of 11/23/09) has a speedy scan rate, that wasn't enough to offset its unimpressive protection from malware infections and its truly annoying interface. With a last-place showing in our stand-alone antivirus rankings, it's clearly a less than ideal choice for your paid protection. (A new version is coming early next year--see the end of this review.)

Avast's ability to block Trojans, worms, and other baddies in AV-Test.org's huge "zoo" of collected malware wasn't bad--its detection rate stands at 97.8 percent--and the program proved particularly adept at blocking worms with a 99.5 percent block rate. But most of the other programs outperformed it; Avast was only good enough for eighth place in signature-based malware detection.

In heuristic tests using two-week old signature files to simulate detection of newer malware, Avast was genuinely bad: A sad showing of 38.5 percent puts the program from Czech Republic-based Alwil firmly in last place among tested products. And it was unable to stop completely new and unknown malware based solely on how these invaders behaved (neither could a few other apps). Considering the short lifespan of the typical piece of malware and how quickly modern malware evolves, being able to detect these digital interlopers before a full signature is issued is more important than ever.

While Avast may not be especially thorough, it is fast. It performed automatic "on-access" scans (scans that happen when you open, save, or download a file, for instance) at a rate of 14.8MBps (megabytes per second); only Avira's AntiVir could match this scan rate. And when faced with existing infections, it proved able to get rid of all active components. However, it left many less-important system changes and malware files still in place.

Avast's performance results had ups and downs, but its interface was just a downer. As with its free program, Alwil's paid Avast Professional edition splits the interface into two entirely different sections: one for settings and one for scans. Double-clicking the system tray icon brings up a so-called "resident protection window" with settings for eight different "shields," such as the Web shield or Internet mail shield. The settings and status interface is relatively straightforward, but it lacks any context-sensitive help to take you straight to the relevant documentation for what you're looking at, forcing users to search for what they need.

Running a scan involves right-clicking the system tray icon and choosing "Start Avast! Antivirus," instead of the aforementioned settings pages. The resulting new interface mimics a music player and is entirely different than the settings window. It's telling that Avast feels it necessary to pop up a page of instructions on how to start a scan every time you open the scanning interface. The Pro version adds an enhanced interface you can use instead of this clunky player panel, but while it's somewhat less annoying, it's not a huge improvement.

It gets worse. When you do figure out how to run a scan, Avast will pop up a warning for every potential baddie it finds, requiringyou to tell it what to do. And you might be forgiven for not realizing that clicking the "Continue" option will cause Avast to ignore the discovered malware and leave it in place.

Alwil says that a new version of Avast due early next year revamps both the interface and the antivirus engine. We look forward to those upgrades, but in the meantime, you're better off checking out the competition.