spyware 
The derogatory term for user-tracking software that is installed on a computer without the user's knowledge. It can be installed on a system by an employer, or it can be included in free software available on the Internet, such as games, utilities, or file-swapping programs. To create revenue, some makers agree to let third-party software--in this case, software that gathers user information that can be used for advertising or marketing purposes--"piggyback" on their software. The third-party software installs along with the requested program. Notification of the additional software is usually buried in a lengthy licensing agreement that the user must accept to get the program. The spyware continues to run in the background even when the program is closed, and uninstalling the original program doesn't necessarily remove the spyware. A similar type of software is called adware.