Spyware is any technology that aids in gathering information about a person or organization without their knowledge. Spyware is software that is installed on someone's computer to secretly gather information about the user and relay it to advertisers or other interested parties, including hackers. Spyware can be installed on a computer as a virus or as the result of installing a new program. Data collecting programs that are installed with the user's knowledge are not, properly speaking, spyware, if the user fully understands what data is being collected and with whom it is being shared. However, spyware is often installed without the user's consent, as a drive-by download, or as the result of clicking some option in a deceptive pop-up window.

The cookie is a well-known mechanism for storing information about an Internet user on their own computer. However, the existence of cookies and their use is generally not concealed from users, who can also disallow access to cookie information. Nevertheless, to the extent that a website stores information about you in a cookie that you don't know about, the cookie mechanism could be considered a form of spyware.

Spyware has become one of the biggest causes of software issues with computers. These programs can go so far as to disable your Internet connection. However, they most frequently cause random pop-ups, abnormal browsing behavior and system lockups, in addition to causing the computer to slow down dramatically.