Has your computer ever become so slow that you can fix yourself a snack in the time it takes your word processor to open? Perhaps spyware is to blame.

Spyware is a category of computer programs that attach themselves to your operating system in nefarious ways. They can suck the life out of your computer’s processing power. They’re designed to track your Internet habits, nag you with unwanted sales offers or generate traffic for their host Web site. According to some estimates, more than 80 percent of all personal computers are infected with some kind of spyware.

Some people mistake spyware for a computer virus. A computer virus is a piece of code designed to replicate itself as many times as possible, spreading from one host computer to any other computers connected to it. It usually has a payload that may damage your personal files or even your operating system.

Spyware, on the other hand, generally isn’t designed to damage your computer. Spyware is defined broadly as any program that gets into your computer without your permission and hides in the background while it makes unwanted changes to your user experience. The damage it does is more a by-product of its main mission, which is to serve you targeted advertisements or make your browser display certain sites or search results.