I don't know about you, but I resent being surveyed involuntarily. I studiously avoid poll takers waiting to ambush me at train stations and supermarkets, and I hang up on telephone surveys. I am the worst nightmare of the Harris, Gallup, and Zogby polling organizations.

So you can understand why tiny software apps that track my behavior online--and are often secretly embedded deep within my Windows system Registry--really raise my ire. Along with violating my privacy, this software can degrade my system's overall performance.

Get rid of them
If you ask me, these apps, called adware or spyware, have no business being on anyone's desktop. That's why I'm pleased to share with you a new and completely free product that will remove them from your PC: Spybot Search and Destroy.

But first, I should explain the subtle differences between adware and spyware.

Adware is software that's included with larger applications, such as games or file-sharing programs, that are free because they require you to look at advertisements. The end-user license agreements for these ad-supported applications clearly state that you will provide the advertisers with some statistical information in exchange for being able to use the products. As you install the main app on your system, the adware embeds itself in your system Registry, collects the URLs of Web sites you frequent, then sends that information back to the advertiser. This info supposedly helps advertisers better target their clients' ads.

Spyware also installs itself on your PC along with other apps and provides advertisers with information about your Web activities, but it does so without your consent. You may download a piece of software that includes spyware and never know it's there until you happen to get a message from your firewall software saying the spyware is trying to contact the Internet.

A list of known adware and spyware vendors and products can be found on various sites around the Internet, such as this one.

Special software needed
Unfortunately, the usual antivirus and firewall programs can't protect you from adware and spyware. Antivirus apps won't detect these pests because they aren't technically viruses. And firewalls block only outgoing messages from adware and spyware; the components themselves remain deep within your PC.

But fortunately, there is other software that can help you. For years, my favorite anti-adware and -spyware app was Lavasoft's Ad-aware. This product can, in a matter of seconds, identify and remove ad-surveying software embedded inside your PC. There are a few negative (depending on your perspective) consequences. For example, some programs dependent on adware or spyware will simply stop working. But that's a risk I'm willing to take.

So what changed? In late January, Lavasoft released its long-awaited Ad-aware 6.0--and added a $40 price tag. Now, the free version of Ad-aware is virtually the same as version 5.0, and to get the new of the new enhancements, you have to pay the $40.

This fee, though admittedly not very high, started to seem less worth it the more I learned about a new, free program called Spybot Search and Destroy. Spybot not only identifies and removes ad-surveying apps embedded on your PC, it also spots Trojan horses, dialers (apps that use ActiveX to dial expensive 976 telephone numbers), security leaks within Microsoft's Internet Explorer, and other malicious behavior on your PC.

Free your PC
Spybot offers significant advantages over the free version of Ad-aware, too. Unlike Ad-aware, which doesn't give you any information about what it finds on your PC, Spybot provides you with a clear list of everything it's discovered. Simply mouse over any item on the list, and you can find out where it came from, what it does, and what Spybot recommends you do--keep it or destroy it.

In addition, Spybot comes with a file shredder that overwrites deleted files with random characters, making it hard for someone to read them later. It gives you a detailed view of what's currently running on your PC (from ActiveX components to individual processes). And it provides an easy way to opt out of direct marketing e-mail so that you can reduce the amount of spam you receive.

As abolitionist Wendell Phillips once said, "Eternal vigilance is the price of liberty." Because we're free to use whatever software we want on our computers, it's up to us to prevent others from controlling our desktops in ways we don't approve of. For now, Spybot is the best tool I know of to aid this cause. As I find new products that keep your computer secure and your information private, I'll keep sharing them with you.

Are you concerned about adware or spyware on your PC? Why or why not? TalkBack to me!

Senior Associate Editor Robert Vamosi covers hoaxes, viruses, and security threats for CNET Reviews. Have a question for him? Let him know!