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Spyware

Spyware is computer software that aids in gathering information about a person or organization without their knowledge. The most common use of spyware is to gather information about the user and relay it to advertisers or other interested parties, but it has been used by law enforcement to collect evidence against criminal suspects.

Spyware can be installed on a computer by a virus, by an e-mail trojan such as the United States FBI's Magic Lantern program, or it may be hidden within the otherwise-innocuous installation a new program. Data collecting programs 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.

The HTTP cookie is a well-known mechanism for storing information about an Internet user on their own computer, often used to assign webite visitors an individual identification number for subsequent recognition. 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 Web site uses a cookie identifier to build a profile about the user, who does not know what information is added to this profile, the cookie mechanism could be considered a form of spyware. For example, a search engine website could assign a user an individual ID the first time he visits and store all search terms in a database with this ID as a key on all subsequent visits (until the cookie expires or is deleted). This data could be used to select advertiserments to display to that user, or could (legally or illegally) be transmitted to third parties.