Spyware is a term for parasitic programs which secretly use a user's internet connection without their permission or knowledge to hide on the user's computer and spy on what they do - including tracking surfing patterns.
Spyware is often attached to software downloaded from the web while hiding the details in the small-print in the license agreement that most users click through without reading!
The implications of spyware sound scary, but it is more of a pest than a serious problem.
A likely symptom is the display of ads on the infected computer, although spyware can go unnoticed until it eventually slows your machine down and causes it to crash.
The best preventative action you can take is to install a firewall that will prevent anything using your Internet connection without you knowing it.
And if you think you have an infection note that Microsoft have recently released a free spyware checker
which you can download it from here
