My stepson Emmet's 13th birthday present from me this summer was a video camera. He's been "making movies" using the Logitech QuickCam attached to his PC for the last six months, and it was high time for an upgrade. Instead of loading the bundled software onto his computer, however, he went straight to my computer to do the job. Why not use his own? It doesn't work, he said. Of course not. It has been a few weeks since I cleaned his. Unfortunately, PCs still aren't owned as much as they are constantly maintained.

These days, it isn't enough to get your kid his own system to keep him from screwing up yours. You have to do the maintenance, too. For me, this means monthly sessions at each PC in the house, removing unused applications, updating virus definitions, purging spyware, and maybe defragging the drive for good measure. It is a pain, but in return I get a solemn promise that no one installs anything on the family's primary (read "my") system.

This isn't just required for kids and teens; there are plenty of adults out there who clutter up their hard drives with "free" screen savers and other spyware-packed applets. If you have the misfortune of living with one of them, cleaning that mess up is probably a job you will have to do.

Now, if I just install one of the big, all-in-one security suites, such as Norton 360, I could probably just set it and forget it. But that gets expensive when you need to install it on every system in the house. Besides, there are free alternatives.

Just logging on to Emmet's computer is a taxing experience. First of all, one of his "friends" had gone on his system and unhelpfully renamed all of the files on his desktop with politically incorrect phrases that I am not allowed to print here. Aside from being moronic, this rendered many of them impossible to open. All those had to go into the trash.

Then there is the matter of Dr. Dre's head. The iconic rapper's image is currently the cursor icon on Emmet's desktop. This is compliments, I think, of a resource-hungry software app called the Mission Impossible 2 Cursor Library (mi2curp.exe). That sounded a little shady. Sure enough, after checking the virus log, I discovered that is how a Trojan horse (dropper.Agent.BMH) snuck into his system a few months back. Fortunately, AVG AntiVirus Free Edition was able to find and quarantine it.

Next up, the spyware. After grabbing the latest definitions for Ad-Aware 2007 (I had to do this manually because I am using the free version), I ran a nice, deep scan. It takes 20 minutes, but it finds lots of junk, including 55 tracking cookies and the Starware Toolbar, which hijacks the IE Search Assistant and the 404 error page and sends you to its own search site. All of that goes.

After those initial scans, I open the Task Manager and see what processes are running. I can see that something called "rlvknlg.exe" is using a lot of resources, so I Google the file name. It is listed as a Trojan on a lot of message boards and seems to be the work of market research firm Relevant Knowledge. The application collects demographic information, survey responses, system info, and Internet usage data, and sends it back to headquarters. It takes a ton of system resources and also delivers some annoying pop-ups.

Don't worry about privacy, though. The company has a detailed policy paper on its Web site that promises, among other things, "All persons installing this application must be at least 18 years old and must be the parent or legal guardian of any minor that may use a computer with this application installed." Sure, so how exactly did it get loaded on my 13-year-old's system? Delete.

A quick check for disc errors, an overnight defrag, and I am done. Suddenly, the PC "works again"--after just three hours of maintenance. Of course, if these steps don't work there is always the "nuke the planet from space" option. Back up the data (there could be some great stuff in those QuickCam movies), reformat the hard drive, and reinstall the OS. It is an extreme measure just to purge a system of viruses and spyware, but sometimes it is the only way to be sure.