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As W32.blaster, Sobig, and earlier virus threats have shown, the Internet is not a terribly safe place to connect your PC. Besides updating Windows and your Internet applications regularly, please, I beg you, install two key utilities--a firewall and antivirus software--to ward off future attacks. And if you install any of the products I recommend below, the ounce of prevention won't cost you a dime.

In last month's column ("Ultimate Network Security: How to Install a Firewall"), I recommended a quartet of effective no-cost firewalls. If you'd had one of those apps running on your PC when Blaster hit in August, you'd have escaped the worm's effects. Free antivirus utilities have been around for a while, but I've never felt comfortable recommending them because testing organizations such as Virus Bulletin and ICSA Labs hadn't endorsed them. To pass the tests administered by these labs, an antivirus utility must, among other things, stop all viruses known to exist in the wild, on demand (during manual or scheduled scans of the hard disk and memory) and on access (using memory-resident shields to block viruses from loading into memory).

How the Free Four Score

Up-to-date performance test results for free antivirus programs aren't always easy to come by, but the little information I've been able to dredge up indicates that most of these utilities are improving. I tried all four of the programs below--the only free Windows antivirus programs I could find--and though I found Grisoft's AVG and Alwil's Avast 4 to be the most feature-rich, I feel comfortable recommending any of the four. They all update their virus definitions automatically and have a seal of approval from at least one testing lab.

Grisoft's AVG Anti-Virus System: AVG passed Virus Bulletin's June 2003 VB100 Windows XP test (the most recent available at press time) after failing previous attempts; it also passed ICSA's June 2003 test. AVG includes memory-resident scanners, plus e-mail scanners for Outlook, Outlook Express, Eudora, and Exchange client.

Alwil's Avast 4 Home Edition: Avast likewise passed both the VB100 and ICSA tests, and it offers memory-resident scanning. But Avast surpasses AVG by scanning both Outlook and standard Internet (POP3/SMTP) mail, making it a good choice if you use a non-Microsoft mail client. Amazingly, Alwil also offers support via e-mail for its free product.

H+BEDV Datentechnik's AntiVir Personal Edition: This utility doesn't appear in Virus Bulletin's June 2003 tests; it did, however, pass ICSA's June 2003 tests. AntiVir includes a memory-resident scanner, but it lacks e-mail scanning (it watches only file read and write operations and looks for suspicious macros). You can use AntiVir's separate scheduler program to launch scheduled hard-disk scans, and virus-signature and program updates; but how to perform these tasks (or whether they're possible) is far from obvious.

Softwin's BitDefender Free Edition Version 7: BitDefender Free Edition does not appear in the VB100 and ICSA test results, but the Standard Edition passes both tests using the same scanning engine as the free version. Like the other free AV tools, BitDefender employs a memory-resident scanner and is set to download updates automatically. But like AntiVir Personal Edition, it doesn't scan e-mail for viruses during send and receive operations.

Set Phasers to Kill

After installing one of these programs, configure it for maximum protection. For example, Avast's heuristics (scanning techniques used to trap new and unknown viruses) are set to medium sensitivity by default. To configure the program for maximum safety, click its system tray icon to open the on-access scanner's settings, and then move the scanner sensitivity slider to High. Click OK (see Figure 1).

The downside of setting an antivirus program to its highest security level is that it might noticeably slow PC performance. If you're stuck with an older machine, you may need to go with the default security settings, or try one of the other three freebies to see if it has less impact on performance.