What is adware?
Adware is any software application in which advertising banners are displayed while the program is running. The authors of these applications include additional code that delivers the ads, which can be viewed through pop-up windows or through a bar that appears on a computer screen. The justification for adware is that it helps recover programming development cost and helps to hold down the cost for the user. Adware has been criticized for occasionally including code that tracks a user's personal information and passes it on to third parties, without the user's authorization or knowledge. This practice has been dubbed spyware and has prompted an outcry from computer security and privacy advocates.

What is spyware?
On the Internet, spyware is programming that is put in someone's computer to secretly gather information about the user and relay it to advertisers or other interested parties. Spyware can get in a computer as a software virus or as the result of installing a new program. Data collecting programs that are installed with the user's knowledge are not, properly speaking, spyware, if the user fully understands what data is being collected and with whom it is being shared.

The above information was largely obtained from whatis.com

Common Spyware / Adware Applications
Spyware and Adware programs can be found in many places.  Spyware usually is installed along with other programs such as KaZaa or Morpheus.  Here is a short list of some common Spyware programs.

• Gator
• BargainBuddy
• BDE
• Bonsai Buddy

A good resource for reading more about spyware is www.spywareinfo.com

How can I get rid of adware/spyware?
Two programs that are good for removing this software are SpyBot Search&Destroy and Ad-aware. Instructions for both of these programs can be found below, along with links to download these tools from download.com.

NOTE : Uninstalling adware/spyware can cause some programs to stop working, such as KaZaa. If you are running KaZaa and want to keep it on your computer, you should open KaZaa so that it is running in the task bar (you'll be able to see the KaZaa icon near the clock on the bottom right of your screen). Run these programs and then highlight all items that you want to remove from your computer and click next. The program will prompt you to delete the items (as shown below), but will be unsuccessful at deleting the items that KaZaa needs to run. When it prompts to delete the items after rebooting, choose "no" and KaZaa will continue working. If you decide that you no longer want to run KaZaa, you should uninstall it before removing these ad/spyware components, because removing these components will prevent KaZaa from uninstalling successfully.
If you have already deleted these items and now cannot uninstall Kazaa, you need to reinstall it, and then it will uninstall successfully.

SpyBot Search & Destroy - download from download.com

To run the program, click "Check for problems." The program will begin scanning your hard drive.

When the scan is complete, a complete list of all the adware/spyware components in your system will be displayed. There will be checkmarks in some, but possibly not all of the boxes. You can check the unchecked boxes, and when you have checked all the components that you want to delete, click on the "Fix selected problems" button.

Upon completion, there will be green check marks beside all components that were successfully deleted. Some components may not have been deleted, especially those of programs that are currently running. If you have KaZaa open, for instance, you will notice that all ad/spyware associated with KaZaa will not have been deleted. You will be prompted to reboot your computer and scan again, but if you do this, some programs may stop working (read the NOTE above).
 

Ad-aware - download adaware from download.com

To run the program, click "start".

After the completion of the program, the "Scan complete" bar will have reached 100%, and you should click "Next".

You should place a checkmark by the items you want to delete (usually all of them, but this could potentially cause some programs to stop working, as stated above).