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Trojan horses. Rootkits. Botnets. Keyloggers. These terms might not mean much to the average computer user, but to the average computer they're the equivalent of the bird flu and Ebola viruses. With money serving as the main motive, tech crooks have turned these one-time playthings of maladjusted geeks into a serious business.

To see which programs offer today's best protection, we tested eight stand-alone antivirus apps: Alwil's Avast 4 Antivirus Professional Edition, BitDefender's Antivirus 10, Eset's NOD32, Grisoft's AVG 7.5 Anti-Virus Professional Edition, Kaspersky's Anti-Virus 6, Panda's Antivirus 2007, Symantec's Norton AntiVirus 2007, and Trend Micro's AntiVirus plus AntiSpyware 2007. These apps allow users to pick and choose their other security software (such as firewalls), and they cost less than security suites. All include antispyware protection, and many have antirootkit components to defend against devious attempts to hide malware deep within a system. To protect against unknown viruses, all of the apps we tested come with some form of proactive protection to supplement more-traditional signature-based approaches, which must match incoming threats against a database of known threats in order to block them. For more information about proactive protections, read "When a Signature Isn't Enough."

After rigorous analysis, we awarded Kaspersky's well-designed Anti-Virus 6 the Best Buy. It ended up in a virtual dead heat with the entries from Symantec and BitDefender for best malware detection honors, and it also did the best job of cleaning malware infections. At $50, however, it's relatively expensive.

In partnership with security research company AV-Test.org, we tested the programs under Microsoft Windows Vista Ultimate; all eight have a Windows XP version as well. By far the most important tests that AV-Test conducted pitted each app against a "zoo"--a collection of nearly 900,000 viruses, Trojan horses, bots, and other forms of malware. After this, each app had to try to detect current threats using one- and two-month-old signature files to simulate how well it could block unknown malware. Our three best-rated apps were, not surprisingly, those that performed best in these critical tests.

We also rated each program on its design and ease of use, including whether the application installed with an appropriate default configuration. We then factored in performance, support policies, and whether the app had features such as Web-traffic scanning. Finally we rated cost. (Read more details on our testing.)

To choose our contenders, we selected from Vista-ready popular sellers and best-of-breed programs. Alwil and Grisoft offer feature-limited free versions of their programs--but to compare apples to apples, we selected their paid versions. Wondering why McAfee isn't on the list? The company no longer sells a stand-alone antivirus app (its VirusScan Plus programs include a firewall). Another no-show is F-Secure, whose popular app wasn't Vista-ready in time for inclusion in our testing.