Spyware is a general term used for software that performs certain behavior such as advertising, collecting personal information, or changing the configuration of your computer, generally without obtaining your consent.

Spyware is often associated with software that displays advertisements (called adware) or software that tracks personal or sensitive information.

It does not mean that all software which provides ads or tracks your online activities is bad. For example, you might sign up for a free music service, but "pay" for the service by agreeing to receive targeted ads. If you understand the terms and agree to them, you may have decided that it is a fair tradeoff. You may also agree to let the company track your online activities to determine which ads to show you.

Other kinds of unwanted software will make changes to your computer that can be annoying and can cause your computer to slow down or crash. These programs have the ability to change your Web browser's home page or search page, or add additional components to your browser you do not need or want.

These programs also make it very difficult for you to change your settings back to the way you originally had them, such types of unwanted programs are also often called spyware.