Getting a Web browser, e-mail program or photo organizer as free software on a computer is routine, but an anti-virus utility for Windows, the target of tens of thousands of viruses and worms? That seems the kind of thing for which you'd want to pay.

But you don't have to. For several years, two Czech software developers have offered free versions of their anti-virus programs to home users. These no-charge downloads don't offer every feature provided by McAfee Inc. and Symantec Corp., the two security developers whose programs come pre-installed on most Windows PCs. But when put to the same tests as software from the Big Two, they did the job almost as well and with less fuss.

Both of these freebies -- Avast 4 Home Edition, from Prague's Alwil Software, and AVG Free Edition, from Brno-based Grisoft Inc. -- can be installed only on home computers that aren't put to any business or commercial use. (Income from sales to businesses and organizations covers the cost of this exercise in Internet charity.)

These two programs share a few welcome traits. Both are relatively small downloads -- almost 10 megabytes for Avast, just under 15 for AVG -- that tout compatibility with systems as old as Windows 95. And both automatically download updates every day and allow quick manual updates.

With Avast (www.avast.com/eng/free_virus_protectio.html), the major selling point is a greater sense of security. After a refreshingly fast install, Avast automatically scans your computer for trouble before allowing Windows to boot up -- a helpful precaution if the computer may already be infected.

From then on, Avast's virus warnings are quick and unambiguous, if thoroughly annoying. When you try to run a virus, a large window, illustrated by a flashing radioactivity icon, will alert you as a warning siren sounds and a recorded voice intones "Caution, a virus has been detected."

That window, however, doesn't make any of its options -- ignore the virus, delete it or move it to a "chest" of quarantined files -- a default action, so hitting the Enter key just cues up the racket again.

Avast's scanning stopped viruses delivered through e-mail (in the Outlook, Outlook Express and Mozilla Thunderbird e-mail programs), Web downloads and instant messaging (old and new releases of AOL's AIM software). It also stopped me from sending out copies of viruses via e-mail in all three of those programs, but it didn't block one transferred via IM.

Unfortunately, it took Avast an extra day to start catching this week's "Sober" virus -- automatic updates did not add that to its database until Tuesday.

Avast's systemwide scans went by relatively quickly, taking 27 minutes to do a routine check of a well-used ThinkPad and an hour and 40 minutes for a full scan. It took just 9 minutes and 37 minutes to run the same tests on a barely used Toshiba.

You can also verify an individual file by right-clicking it and selecting Avast's "Scan" command. But it's hard to know that it's been judged safe until you realize that Avast's scan window closes instantly if it doesn't spot any trouble.

That ill-thought-out behavior reflects a deeper problem with Avast's interface -- that it's a mess. The program offers three distinct looks in various parts (its system-scan window appears to have been patterned after old MP3 programs like Winamp), and finding settings like the one to silence the audio alerts takes some digging.

Avast offers tech support only via e-mail -- not that Symantec and McAfee are much more generous. (The only major anti-virus program with free phone support is Trend Micro's PC-cillin.)

AVG (free.grisoft.com) doesn't even offer help via e-mail. But it makes up for that in other ways.

This program installed quickly and then blocked access to every virus without any goofy sound effects. Unfortunately (just like in Avast), AVG's "Virus Detected!" window fails to make deleting or at least quarantining a virus the normal action -- and if you do elect to delete it, the default choice in a second dialog is "no."

Microsoft Outlook users need not worry about that problem, though; AVG's Outlook plug-in automatically quarantines viruses as they show up in e-mail.

This program wasn't quite as disciplined with Outlook Express and Thunderbird. I could save attached viruses to the hard drive, and I could forward messages with viral payloads (although my Internet provider's own virus scanners rejected them). I could also send and download viruses via AOL instant messaging.

But in no case could I run a virus; AVG stopped that every time.

AVG's systemwide scans took anywhere from one and a half to twice as long as Avast's.

But when I scanned an individual file, AVG clearly identified it as safe. AVG's interface is in general far cleaner than Avast's, putting all the relevant controls and status indicators in one window.

Neither program's screening was quite as far-reaching as that offered by competitors -- for example, Avast and AVG allowed me to preview a .zip archive containing a virus using Windows XP's Compressed Files tool, while Symantec and McAfee's software denied all access to that .zip file.

Also, neither Avast nor AVG will stop spyware that you choose to download and install on your own -- each pronounced a freebie, spyware-riddled download as safe. So you'll still need a separate anti-spyware utility such as Microsoft's free Anti-Spyware for Windows 2000 and XP.

But if you define an anti-virus utility's job as ensuring that no virus sent your way can run on your computer (as opposed to also ensuring that no virus can even land on your computer), these two programs were just as capable as their pricier competitors. And while I've gotten more reader reports than I can count of PCs immobilized by malfunctioning Symantec and McAfee software, I've yet to hear of such trouble with Avast or AVG.

Whichever virus scanner you use, make sure you keep one other active -- the one that came pre-installed at birth: your brain.

Even the most rigorously updated security software can miss a just-created program that hasn't been entered into virus databases, but any reasonably aware human should still be able to spot a con job when it arrives.

Be as skeptical and smart about strange files as you would any other strange solicitation, and you won't have to rely on somebody else's software as your only line of defense.

Living with technology, or trying to? E-mail Rob Pegoraro at

rob@twp.com.

Avast's virus warnings are quick and unambiguous, if annoying.The home version of Avast is free; businesses must pay.AVG's interface is in general far cleaner than Avast's.