Spyware: Spyware is software that gathers information about a person or organization without their knowledge, and may send that information to another entity without the consumer's consent. Spyware can collect almost any type of data, including personal information like Internet surfing habits, user logins, and bank or credit card information. Spyware is classified into four types: system monitors, trojans, adware, and tracking cookies.

Spyware can also sometimes assume control over a computer without the consumer's knowledge. Spyware can interfere with user control of a computer by installing additional software or redirecting web browsers. Some spyware can change computer settings, which can result in slow Internet connection speeds, un-authorized changes in browser settings, or changes to software settings.

When spyware is used for malicious purposes, its presence is typically hidden from the user and can be difficult to detect. Some spyware, such as keyloggers, may be installed by the owner of a shared, corporate, or public computer intentionally, in order to monitor users.

Spyware is a costly problem, but a number of techniques have emerged to counteract it. These include spyware removal programs, blocking programs, as well as many user practices which reduce the chance of getting spyware on a system. Many major anti-virus firms, like Symantec, PC Tools, McAfee, and Sophos have also added anti-spyware features to their anti-virus products. Computers running Windows programs are most susceptible to spyware, and even some spyware cannot be removed by spyware removal programs. Sometimes the only solution is to fully reinstalling the operating system.

Unauthorized access to a computer is illegal under computer crime laws, and since owners of computers infected with spyware generally claim that they never authorized an installation, this seems to violate these laws. However, spyware producers often hide descriptions of the spyware programs within the legalese text of an end-user license agreement, which many users habitually ignore, and agree to without reading. However, Spyware companies say these demonstrate that users have consented.