Spyware and adware are small programs that install themselves on your computer. They track your surfing habits and collect personal data that's then sent back to their creators. They can run behind the scenes on your computer and you might not even know that they're there.
You may have unknowingly installed spyware when you visited websites or downloaded programs from the Internet. Detecting and removing spyware and adware is included in most PC security packages including BT PC Security.