There are a lot of programs that will clean the nasties off your PC, but SpyBot Search and Destroy from PepiMK Software is my favorite.

Don't take my word for it, here are some testimonials from their website:

• Suzanne S.: Thanks for the Spybot S&D software, Patrick! It's helped me clean up my computer and I feel confident that I have a weapon to protect myself from some of the online predators out there who want to sleaze their way into my personal information.
• Jeff K.: Thank you for providing such a feature rich product. I hope everyone else realizes that $10 or whatever they can afford for a commercial quality product that protects a $1000 investment and up is a bargain. Keep up the good fight.
• Matthew P.: My computer was staggering under the weight of so much spyware. Your software brought it back to life! I now run it weekly and things run much smoother. It's great!

There is an Immunize function that alows you to block all of the nasties that Spybot knows about, and that has helped prevent many an installation!

Another program that does a good job of cleaning your PC is AdAware from Lavasoft. With the release of Ad-Aware SE Personal edition, Lavasoft takes the fight against Spyware to the next level. The scanning is faster, and there is a code recognition piece that helps protect against new variations of some known nasties. AdAware consistently ranks as the top AntiSpyware download at Download.com.

As good as these two programs are, they do not always manage to get rid of browser hijackers from the Cool Web Search hijackers. If you have a persistent problem with your home page being changed, try CWShredder from Intermute. The download page is located here. Merijn Bellekom of Spyware Info wrote the program and kept it updated as long as he could, but the fight was costly in terms of time and money. Fortunately, Intermute licensed the code for their X-Cleaner AntiSpyware program and have continued to update CWShredder.

Warning! There are a number of programs that pretend to be spyware removers when they actually add spyware to your system. If you get an email or popup ad that indicates the program being offered will scan your computer for spyware, DO NOT USE IT. More often than not it will "find" spyware on your system and recommend that you buy the program to clean your computer. In many cases the scan actually installs spyware just so that you will feel justified in shelling out your money. ALWAYS double check by running AdAware or SpyBot before you pay anything for a program to clean your computer.