With downloadable software, free doesn't always mean without cost. Many software companies resort to bundling free applications with spyware and adware programs for a cut of advertising money from third-party companies. These unwanted guests can slow down your system, track your Web-surfing habits, and even record private information. That's why it's so important to have the best spyware detectors available to root out these parasites before they choke your system.

To help you decide which programs to use, we assembled a spyware-detector obstacle course of the most nefarious spyware and adware available: nCase, BargainBuddy, ISTbar, DyFuCA, PowerScan, and Internet Optimizer--the Unsavory Six.

We then ran the most well-known heavyweights in the adware-removal category, including the free programs Ad-Aware and Spybot - Search & Destroy, as well as the paid programs Spy Cleaner Gold, Spyware Doctor, and Webroot Spy Sweeper, to see how well each performed.

We certainly liked it when our Unsavory Six showed up on the detection list, because it showed the program was thorough about listing each culprit. However, it was far more important that it remove the programs from our hard drive. We held the paid software to a higher standard because you need to pay if you want the full version or updated definitions.