Spyware is dangerous for a number of reasons. Spyware may steal sensitive information. Spyware consumes your computer's resources and makes the performance of your computer slower. By using the autorun function of your PC it will also make your computer's startup take longer. Some of the malicious applications install themselves as plugins for your web browser, adding annoying pupups and message windows to your browser's features. Some spyware apps send stolen data to their home servers, which make your Internet connection slower and increase traffic consumption. Also, most of these programs are poorly written and contain bugs, which make your overall system performance unstable.

Spyware is usually installed along with freeware or shareware applications distributed over the Internet. You may get spyware when you download music or software using file sharing networks. Sometimes even opening a web page can lead to spyware installation. By the way, please make sure that you never click "OK" when a web site pops up a window offering you to install something.

It is worth noting that some freeware applications are actually masked spyware. The promise can be different - Internet optimizers, system utilities or even spyware removers. They can even partly perform all these useful functions, but do their malicious work in the background. When installing software, make sure that it comes from a known and trusted vendor or that there are at least several positive reviews of this application on the Internet.