If security software is so necessary in Windows -- as it is -- why are we supposed to pay extra for it?

For years, that's been a paradox Windows users have been able to mull over as they sat through installations of other companies' security software on their computers.

Symantec's and McAfee's security software programs have long benefited from Microsoft's oversights. Both firms supply the antivirus programs offered in trial form on most new PCs -- and which help advertise their full-fledged security suites.

But the 2006 editions of these suites -- McAfee Internet Security Suite 2006, $50 as a download or $70 as a box for Win 98 or newer; Symantec's Norton Internet Security 2006, $70 for Win 2000 and XP -- look unworthy of that success.

For one thing, they face competition from Microsoft, which last year added effective firewall protection to Windows XP with its Service Pack 2 update and has since released a surprisingly good (though still in beta test) anti-spyware tool.

For another, the complexity of the Symantec and McAfee suites seems to cause them to fail in ugly and destructive ways, according to readers who have written in to complain about these problems week after month after year.

Most important, the latest McAfee and Symantec suites just don't work all that well.

Both excel only in their antivirus utilities -- which you can buy separately from these all-purpose bundles. Each program correctly blocked viruses received via e-mail in two different e-mail applications and via AOL's AIM instant-messenger software. Each also automatically fetched updates to its virus database every day.

Symantec's Norton AntiVirus, however, was quicker about its business, cleanly killing viruses with just brief notifications afterwards. Symantec's installer, unlike McAfee's, also scanned the computer for viruses before setting up the program, a sensible precaution.

McAfee VirusScan, meanwhile, asked what it should do every time it found a virus -- as if the choice should ever not be "delete." Downloading antivirus updates manually required setting Internet Explorer as the default browser, turning off pop-up blocking and accepting the installation of an ActiveX program from McAfee's site -- everything you shouldn't be in the habit of doing if you want to stay safe online.

Things get worse in the rest of the McAfee and Symantec suites.

Their firewalls, intended to stop worms from crawling onto your computers, offer no more protection against intrusions than the one in Win XP Service Pack 2. Their advantage comes if a program has already moved in, when they can stop it from communicating with its creators. But these firewalls first need to learn which ones are safe so as not to nag you about the harmless activity of legitimate software.

Symantec's firewall tries to educate itself with a one-week "learning mode," when the firewall watches your use and stops only known offenders. After that, it will flag unknown programs that attempt to contact anything online -- but its default recommendation will be to give them free rein.

McAfee's firewall comes with a whitelist of known-good applications, but this database was laughably incomplete -- among others, it failed to recognize the Mozilla Thunderbird e-mail program, the Spybot Search & Destroy spyware scanner and the WeatherBug forecast look-up tool.

These two suites attempt to police spyware -- programs activated without your consent when you install allegedly free software downloaded from some Internet sites -- but did so no better than free alternatives.

Neither dislodged an infection by one of the most tenacious spyware offenders, Aurora/A Better Internet, but McAfee was particularly woeful. It allowed this parasite to launch repeated pop-up ads -- including one, apparently bought by a third-party retailer, for McAfee's security utilities! -- and was conned by Aurora into blocking access to the download page for Microsoft AntiSpyware.

McAfee and Symantec's filters against phishing (in which thieves set up pages impersonating the Web sites of financial institutions to get you to cough up personal data) seem even less effective. Neither flagged obviously fake PayPal-look-alike scams.

Symantec and McAfee also tout spam filtering, but that applies only if you use the two mail programs they support -- Microsoft's antiquated Outlook Express and bloated Outlook. In addition, their filters assume your e-mail account runs on the Post Office Protocol standard, ignoring a newer, more convenient standard called IMAP.

McAfee's spam filter used an unnecessarily convoluted setup and didn't allow the encrypted login required by a test Gmail account.

The two security bundles can filter out ads on Web pages as well as in e-mail. Symantec's ad-blocking did zap many of the more annoying commercials online, but at the cost of erasing non-ad graphics on occasion. McAfee's ad-blocking, however, routinely dismantled innocent graphics -- including the masthead graphic at the top of The Post's home page -- while allowing plenty of real ads to sail through.

Don't bother with Symantec's weak parental controls. They offer only vague categories of restrictions on Web sites and programs, without telling what it bans in each area (although you can also block individual sites and applications of your choice), and can't enforce time limits on a kid's computer use.

Neither suite is too pleasant to live with when not blocking threats. Symantec's interface works way too hard at selling other Symantec applications, while McAfee's requires opening window after window to check or adjust its many settings. And the two companies' tech-support policies rank among the stingiest ever.

Both charge fees for all phone calls, unless they decide it was their software at fault, and provide only limited access to live help online (McAfee's live chats are as difficult to connect to as its manual update downloads).

If you're running Windows XP, you're better off sticking with the firewall built into SP2, then downloading Microsoft's AntiSpyware and using a mail program with a built-in spam filter, such as Microsoft's Outlook 2003, Qualcomm's Eudora or the free Thunderbird. Then run whatever antivirus program came with your machine. If one isn't active, Symantec is better than McAfee (I plan to review other antivirus utilities soon).

If you're not running XP, go with the McAfee suite for now. But think hard about whether you actually need to run Windows on your next computer. Compared with dealing with these programs, life with Mac OS X or Linux -- both blissfully free of spyware and viruses -- may look awfully appealing.

Living with technology, or trying to? E-mail Rob Pegoraro at rob@twp.com.

The 2006 Symantec (Norton) and McAfee security suites have firewall, filter and fee issues.