Spyware takes many forms and even if you surf with care Spyware can be picked up. Hidden functions in downloaded software, Adware and some types of browser cookies can all be Spyware, storing and sharing information with an un-authorised source.
Spyware can cause all manner of problems on your PC.
If you have been infected with spyware you may notice your PC is running slowly. You may find your Internet browsers homepage or toolbars have changed.