Spyware sits in the background of your computer, watches what websites you visit, then reports on your activities. Based on those activities, targeted ads are delivered to you. But first, the spyware has to get onto your computer. Often, you get spyware by downloading a free program, or clicking a pop-up ad. Spyware comes along for the ride without you knowing it. When you install the program you've chosen, spyware gets installed as well, without telling you.