Countersurveillance refers to measures undertaken to prevent surveillance, including covert surveillance. Countersurveillance may include electronic methods such as bug sweeping, the process of detecting surveillance devices, including covert listening devices and visual surveillance devices. More often than not, countersurveillance will employ a set of actions (countermeasures) that, when followed, reduce the risk of surveillance. Countersurveillance should not be confused with sousveillance (inverse surveillance) as the latter does not necessarily aim to prevent or reduce surveillance.
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Most bugs emit some form of electromagnetic radiation, usually radio waves. The standard counter-measure for bugs is therefore to "sweep" for them with a receiver, looking for the radio emissions. Professional sweeping devices are very expensive. Low-tech sweeping devices are available through amateur electrical magazines, or they may be built from circuit designs on the Internet.
Sweeping is not foolproof. Advanced bugs can be remotely operated to switch on and off, and some even rapidly switch frequencies according to a predetermined pattern in order to make location with sweepers more difficult. A bug that has run out of power may not show up during a sweep, which means that the sweeper will not be alerted to the surveillance. Also some devices have no active parts, an example is the Great Seal given to the US Ambassador to Moscow which hid a device (the Thing).
Most surveillance uses human, rather than electronic methods.
The methods of countersurveillance come straight from the movies and television. Some of these are:
The United States military refers to electronic countersurveillance as "technical surveillance counter-measures" (TSCM) and relates it to ELINT, SIGINT and ECM.
The United States Department of Defense defines a TSCM survey as a service provided by qualified personnel to detect the presence of technical surveillance devices and hazards and to identify technical security weaknesses that could aid in the conduct of a technical penetration of the surveyed facility. A TSCM survey will provide a professional evaluation of the facility's technical security posture and normally will consist of a thorough visual, electronic, and physical examination in and about the surveyed facility.
This definition is however lacking some of the technical scope involved. COMSEC (communications security), ITSEC (information technology security) and physical security are also a major part of the work in the modern environment. The advent of multimedia devices and remote control technologies allow huge scope for removal of massive amounts of data in very secure environments by the staff employed within, with or without their knowledge.
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