) may be viewed in What is spyware?
Spyware is a general term for a class of software that monitors the actions of a computer user, typically without their knowledge. On the Internet, spyware programs may be installed on someone's computer to secretly gather information about the user and relay it to advertisers or other interested parties. Spyware can "infect" a computer as a software 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 as a drive-by download, or as the result of clicking some option in a deceptive pop-up window and may collect information to further attacks on the user's computer or online transactions (e.g. "keylogging" to gain passwords).
Adware, software designed to serve advertisements, can usually be thought of as spyware as well because it almost invariably includes components for tracking and reporting user information. This is one of the most insidious problems currently facing internet users.
It is to be noted that many antivirus products do not provide adequate protection against spyware; it requires installing a seperate spyware-specific product or complete suite from the vendor.
For more information, see the Security Glossary.
