What is spyware?
With so many types of malicious software being spread around the Internet, it is important to be aware of what spyware is and what spyware does. Spyware is a general term used to describe software that performs certain behaviors, generally without appropriately obtaining your consent first, such as:
Spyware is often associated with software that displays advertisements (called adware) or software that tracks personal or sensitive information.
Trading tracking for services
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. You might also agree to let the company track your online activities to determine which ads to show you.
What does spyware do
Knowing what spyware does can be a very difficult process because most spyware is designed to be difficult to remove. 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. They also make it very difficult for you to change your settings back to the way you had them.
How to prevent spyware
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.
A common trick is to covertly install the software during the installation of other software you want such as a music or video file sharing program.
Whenever you install something on your computer, make sure you carefully read all disclosures, including the license agreement and privacy statement. 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.
There are a number of ways spyware or other unwanted software can get on your computer. To learn more about spyware, read How to help prevent spyware.