Spyware is a general term used to describe software that performs certain behaviors such as advertising, collecting personal information, or changing the configuration of your computer, generally without appropriately obtaining your consent first.(What Is Spyware)
Spyware is often associated with software that displays advertisements (called adware) or software that tracks personal or sensitive information.
That does not mean all software that provides ads or tracks your online activities is bad. For example, you might sign up for a free music service, but you "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.(What Is Spyware) You might also agree to let the company track your online activities to determine which ads to show you.
Other kinds of spyware make changes to your computer that can be annoying and can cause your computer slow down or crash.
These programs can change your Web browser's home page or search page, or add additional components to your browser you don't need or want.(What Is Spyware) These programs also make it very difficult for you to change your settings back to the way you originally had them.
The key in all cases is whether or not you (or someone who uses your computer) understand what the software will do and have agreed to install the software on your computer.(What Is Spyware)
Whenever you install something on your computer, make sure you carefully read all disclosures, including the license agreement and privacy statement. (What Is Spyware) Sometimes the inclusion of unwanted software in a given software installation is documented, but it might appear at the end of a license agreement or privacy statement.