What is spyware? Simply, spyware is software that transmits personally identifiable information from your computer to some place in the internet without your knowledge.

Spyware is typically not the product you install itself, but small add-ons, that you may or may not disable during install. In most cases, the EULA somewhere has a few lines telling you about privacy matters, but typically most users don't read the complete EULA and never know they have spyware on their system.

Adware is a less threatening sort of program. Adware is similar to spyware, but does not transmit personally identifiable information, or at least the collector promises not to sell it. Instead, aggregated usage information is collected, and sent somewhere on the internet.

Adware is also often a side-effect of spyware, as both monitor you for a sole purpose – delivering you advertisements that are especially tailored to your habits.

Another kind that is detected under the spyware category is tracking cookies. Cookies are used all over the internet in useful and less useful places. Advertising companies often set cookies whenever your browser loads a banner from them. In that case and if that cookie contains a GUID, the company gets a notice about every site you visit that contains their ads.