According to wikipedia, spyware is defined as "computer software that is installed surreptitiously on a personal computer to intercept or take partial control over the user's interaction with the computer, without the user's informed consent." In basic English, this means that without you knowing it, this program is on your machine, performing various tasks without your informed consent. I use the term "informed consent" because generally consent was given by installing a certain program or on your machine with the intention of performing a task the user wants it to do, whether it is to perform as a file sharing client, edit the appearence of a part of the desktop, or other suchuser desired tasks. Through that consent that the user freely gave, however, the consent was also given to install anything bundled with it, which generally performs non-desirable tasks such as mining personal data, displaying ads out of the blue, or hijacking web browser functionality to the program publisher's benefit. This non-informed consent transaction can also take place on websites which prompt the user to install some piece of code in their browser to seemingly improve the functionality of the website he or she is visiting.

I have listed links to various spywareremoval programs below, please visit the sites and choose the one right for you: