Computers are instruments that send, receive, and process information. Computers must be programmed to perform these functions, and many of the functions they perform are critical to an operation or the financial success of a business. These reasons make computers both a target for those seeking illicit information, and as a means of monitoring the activities of the users of a computer or a computer network. Such illicit activities are popularly known as computer espionage.

Computer espionage extends from an individual's personal computer to sanctioned government initiatives. At the local level, software exists that allows a personal user or a company to monitor the activity of any computer that the software can access. Some programs are capable of recording the keystrokes a user makes while at the computer, or at a Web site.

Every video display terminal emits radio frequency waves. These can be detected using...