It happens all the time to unlucky or unwise Windows users: A new computer crashes and burns after a crippling virus or worm attack. But things can fall apart inside a new PC without such outside help; everyday use can cause a slower form of rot that eventually hobbles the system as thoroughly as a virus might.

An antivirus program alone isn't enough to keep a PC in good health these days. A comprehensive security program includes firewall software, spyware defenses and diagnostic and repair tools to fix the routine wear and tear of Windows. And this kind of all-in-one package needs to do this without becoming a problem itself by slowing down your system.

Symantec largely defined this category of software with its Norton SystemWorks bundle, but it also has earned a reputation for invasiveness, flooding users' screens with warnings and alerts. The 2005 edition finally addresses this problem, drastically reducing its nag factor while keeping its broad reach -- beyond virus and firewall protection, it includes a password manager, a program uninstaller, system-repair and optimization tools and a system-restore program.

SystemWorks 2005 (Win 98 or newer, $70, plus $20 annually for antivirus updates after one year) does almost everything in the background and automatically. A "One Button Checkup" option runs all of its tests, getting the latest antivirus profiles and checking your Windows registry -- a systemwide database of settings that often becomes a source of trouble -- for corrupted or missing entries.

I tested this checkup routine on a gaming-oriented computer that had begun to bog down. In about 15 minutes, SystemWorks found, then fixed, 157 problems; the system ran noticeably faster afterward.

But SystemWorks' spyware-removal capabilities didn't live up to the high standard set by the rest of the suite. When one such parasite infested a test machine, splattering pop-up ads across its screen, SystemWorks identified the offending application but couldn't expel it.

You would be wise to rely on a separate anti-spyware application; not using Microsoft's Internet Explorer browser and being careful about what you download can also help.

McAfee, a perennial runner-up to Symantec, focuses mostly on Internet-borne threats, not day-to-day PC decay, in its RedZone suite (Win 95 or newer, $100). This bundle includes antivirus protection, a firewall, a spyware remover and a spam blocker, but leaves out Symantec's Windows-maintenance tools.

McAfee's firewall is the most impressive part of the bundle; it was simple to set up and provides effective protection without getting in the way of legitimate Internet applications. McAfee's SpamKiller works similarly, cleaning out your inbox after a minimal setup. McAfee's antivirus component is fairly standard; new virus profiles cost $24 annually after the first year of use.

RedZone did beat SystemWorks on the spyware front -- it cleaned out the spyware infection that had eluded its competitor.

Is that worth $30 more than what Symantec charges for its suite? Probably not, considering most users need the system-repair capabilities McAfee leaves out -- and how many free spyware removers, such as AdAware, are available.

Iolo Technologies isn't nearly as well known as Symantec or McAfee, but its System Mechanic 5 Professional (Win 98 or newer, $70) is a worthy alternative to the big two for techies with exhaustive knowledge of their PCs. System Mechanic lets you tweak many obscure Windows settings, such as the time each menu takes to open and the look of the startup and shutdown screens.

This year's release adds antivirus and firewall protection from Kaspersky Labs; the firewall, however, took a bit more work to set up than McAfee's, and the virus protection includes only a year of updates, after which users will have to upgrade to next year's System Mechanic release (the current upgrade price is $40). This suite is a worthwhile alternative for ambitious users, but its power is also a source of peril in the hands of a too-enthusiastic tinkerer.