In a considerable number of countries, special units of secret police security forces exist, acting outside ordinary legal procedures under the supervision of the authorities or with their approval or connivance. In a number of situations, personnel, sometimes called 'death squads', carry out arrests and detention and in many cases kill suspects without any of the legal formalities required by law and without reference to the judiciary. Their activities in most cases are kept secret and outside the control of the judiciary. Information on arrests or detention is not communicated even to the families of the arrested or detained.
Undercover operations can be risky for the agents who spend a lot of time with the criminals. They may become unable to draw a line between impersonating and becoming lawbreakers. After successful undercover assignments these agents suffer from depression, anxiety, lethargy and lack of motivation, even personality changes. Another risk is that the respect for and trust in the administration of justice may diminish, especially if government knowingly bypasses normal restraints and uses disreputable methods, such as deception or videotapes, to gather evidence.
Well-known examples are the German Gestapo, Russian KGB and the secret forces which exist in some Latin American countries.