BitDefender Antivirus 10 nearly took top honors in "Virus Stoppers," our eight-program antivirus roundup. It did an excellent job of detecting malware, with a 96 percent catch rate. It also ranked second in our proactive detection tests (behind Eset's NOD32) using one-month-old signature files, nabbing 61 percent of new malware samples. And at $30, with a $22 renewal fee, it's one of the least-expensive programs we tested.

The program was badly hamstrung by serious slowdowns in our WorldBench 6 Beta 2 application performance tests on Windows Vista Ultimate, however. One Firefox test, for example, which loads a large number of different Web pages, took three times longer with BitDefender than with any other program we tested. The slowdown wasn't debilitating, but it was noticeable. The company says the problem is a known bug in the Vista version that will be fixed in a future program update.

Though it excelled at malware detection, BitDefender was less adept at disinfection. It successfully cleaned just 13 out of 22 items, missing one malware file and both changes to the network settings Hosts file.

BitDefender also had the highest false-positive rate, incorrectly labeling 14 harmless files (out of 20,000) as malware.

On the plus side, BitDefender has a well-designed interface. A slider bar in the main window provides an easy way to modify levels of security protection, and clearly marked icons let you launch full scans and set up custom scans. BitDefender was also the only product to offer free 24/7 phone support, with easy-to-find phone numbers and support e-mail addresses listed in the "Help" section of the application.

By default, the program runs a full-system scan daily. It scans e-mail traffic on the POP3 and SMTP protocols and integrates nicely with Microsoft Outlook, Outlook Express, and Windows Mail (on Vista) for antispam filtering. BitDefender has a basic level of instant messaging protection, but unfortunately it doesn't scan HTTP traffic by default to identify Web-borne threats--you'll need to turn on that capability yourself.

A useful "privacy guard" feature detects when personal information--such as a credit card or Social Security number--is being stolen from a computer, without your having to first tell it what those numbers are. BitDefender was one of the only two programs we tested that automatically disabled Vista's built-in Windows Defender antispyware utility, however. Symantec Norton AntiVirus 2007 was the other.

We tested the Vista version of BitDefender Antivirus 10 for our "Virus Stoppers" roundup. An XP version of the software is also available.

Ryan Naraine