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 of 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 advertisements to display to that user, or could (legally or illegally) be transmitted to third parties.
Another cause is granting permission for web based applications to integrate into your system. These browser helper objects embed itself as part of your web browser.
Spyware is usually installed by some stealthy means. If you read the user agreements for the software you download and install, references (sometimes vague) are cited for allowing the issuing company of the software to record your internet usage and website surfing. Some software vendors allow you to buy the same product without this overhead.
Some incomplete thoughts: Neglect is an additional cause. Use of automatic updates, antivirus, and other software upgrades will protect your system. Software bugs and exploits remain with older software, because the public is more aware how to invade your system.
Commonly Found Spyware
Some spyware commonly found on computers includes:
A number of software applications are available to help computer users search for and remove spyware programs.