Spyware is software or hardware installed on a computer without
user's knowledge which gathers information about that user for later retrieval by whomever controls spyware. Spyware can be broken down into two different categories, surveillance spyware and advertising spyware.
Surveillance software includes key loggers, screen capture devices, and trojans. These would be used by corporations, private detectives, law enforcement, intelligence agencies, suspicious spouses, etc.
Advertising spyware is software that is installed alongside other software or via activex controls on internet, often without user's knowledge, or without full disclosure that it will be used for gathering personal information and/or showing user ads. Advertising spyware logs information about user, possibly including passwords, email addresses, web browsing history, online buying habits, computer's hardware and software configuration, name, age, sex, etc of user.
As with spam, advertising spyware uses CPU, RAM, and resources of user's computer, making user pay for costs associated with operating it. It then makes use of user's bandwidth to connect to internet and upload whatever personal information it has gathered, and to download advertisements which it will present to user, either by way of pop up windows, or with ad banners of ad-supported software. All of this can be considered theft in cases of advertising spyware that installs without disclosure.
