Spyware

noun
1.
Computers. software that is installed surreptitiously and gathers information about an Internet user’s browsing habits, intercepts the user’s personal data, etc., transmitting this information to a third party:
a parent’s use of spyware to monitor a child’s online activities.
2.
tools that are used to conduct espionage:
The nation’s sophisticated spyware rivals that of the CIA.
noun
1.
(computing) software installed via the internet on a computer without the user’s knowledge and used to send information about the user to another computer
noun

any software that covertly gathers information about a user while he/she navigates the Internet and transmits the information to an individual or company that uses it for marketing or other purposes
Usage Note

computing
software
(Or “adware”) Any type of software that transmits information without the user’s knowledge.
Information is sent via the Internet to a server somewhere, normally as a hidden side effect of using a program. Gathering this information may benefit the user indirectly, e.g. by helping to improve the software he is using. It may be collected for advertising purposes or, worst of all, to steal security information such as passwords to online accounts or credit card details.
Spyware may be installed along with other software or as the result of a virus infection. There are many tools available to locate and remove various forms of spyware from a computer.
Some HTTP cookies could be considered as spyware as their use is generally not made explicit to users. It is however possible to disallow them, either totally or individually, and some are actually useful, e.g. recording the fact that a user has logged in.
(http://spychecker.com/spyware.html).
(2004-05-23)