According to a July 2005 Pew Internet & American Life Project report, 68% of internet users - 93 million Americans - experience computer problems that can be traced back to adware and spyware.

There are two types of threats that can be considered spyware:

1. Trojan viruses and “keyloggers” - these malicious programs install themselves on your computer, track your internet activities, and send your personal information back to hackers.
2. Adware - these are programs that spy on your internet activity for the purpose of showing you more relevant advertisements or to redirect you to other websites.

The first type is illegal. The second isn’t but can be annoying and slow your computer to a crawl or prompt pop up ads whenever you’re online.

How To Stop It
According to the Pew report, 91% of internet users say they’ve altered their internet behavior to avoid spyware. According to the numbers

• 81% have stopped opening email attachments unless they are sure they are safe (9% say they never did)
• 54% have started reading user agreements more carefully before they download software
• 48% have stopped visiting certain websites
• 34% have stopped downloading software programs from the internet (while 33% say they never did)
• 25% have stopped downloading music or videos from peer-to-peer networks (48% more say hey never did)
• 18% switched to a different browser

How To Remove It
There are a number of programs out there that will scan your computer for installed spyware and adware and remove it. I highly recommend:

Spybot
LavaSoft’s Ad Aware
Spy Sweeper

I find that it’s generally best to install at least two of them, as one will inevitably miss some stuff that the other will pick up.