Unless you know how to avoid it and/or combat it, you probably have it on your computer.  If you do know about it and scan for it, if you haven't scanned in a while, you probably have something new on your PC.  Just about every PC has something that fits this category running on the PC, eating up resources, or worse yet, spying on your activity, collecting data from you. 

What's the purpose of Spyware?  Why do they do it?  Big Money.  Or at least the potential for Big money.  Lets face it.  There are gullible people out there.  People who will read that pop-up message, maybe even buy something.  The large majority of people will not.  But with millions of PCs out there, the odds are the scumbags that hired the scumbag script writers or programmers will make a few bucks.  While Microsoft is making some progress in fixing the incredible number of security holes in their operating systems, every computer running one of the flavors of Windows, including the latest operating systems from Microsoft, will be affected by Spyware or Adware.

So how do you remove Spyware?

Like it or not, Spyware is a huge industry.  Fortunately there are many great products on the market designed to combat spyware.
 

Here are our top picks:

Spybot Search and Destroy Detects and removes spyware of different kinds (dialers, loggers, trojans, user tracks) from your computer. Blocks ActiveX downloads, tracking cookies and other threats. Scans for over 38,000 objects using detection definitions that are updated frequently. It also provides detailed information about found problems.  Cost is FREE with donations accepted (please donate to their cause if you like the product).
More information including links and tips for using the program.
Ad-Aware SE Personal Ad-Aware Personal provides advanced protection from known data-mining, aggressive advertising, Trojans, dialers, malware, browser hijackers, and tracking components. This software is downloadable free of charge.
More information including links and tips for using the program.
Hijack This HijackThis: A general homepage hijackers detector and remover. Initially based on the article Hijacked!, but expanded with a lot of other checks against hijacker tricks. It is continually updated to detect and remove new hijacks. It does not target specific programs/URLs, just the methods used by hijackers to force you onto their sites. As a result, false positives are imminent, and unless you are sure what you're doing, you should always consult with knowledgeable folks (e.g. the forums) before deleting anything.
More information including links and tips for using the program.

Other Popular Tools:

• Microsoft's Windows Defender
• Spy Sweeper from Webroot Software
• SpywareBlaster from Javacool Software
• HijackThis by Merijn.