What is spyware? To put it simply, spyware is software that transmits personally identifiable information from your computer to some place in the internet without your explicit approval knowledge.

Spyware is typically not the product you install yourself, 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 do not read the complete EULA and never know they got spyware on their system.

A less threatening kind of malware (i.e. malicious software) is adware. 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.

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

Another kind that is detected under the spyware category are tracking cookies. Cookies are used all over the internet in useful and less useful places. Advertisement 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 notice about every site you visit that contains their ads.