Covert surveillance occurs when someone or something is being observed without knowledge. People who are under surveillance are most often under suspicion. Locations and buildings are primarily observed because of suspicious activity or to obtain information about a suspect.
Covert surveillance is generally performed by government agencies, private investigators or business owners. Intelligence organizations such as the Central Intelligence Agency (CIA) of the United States and the United Kingdom’s Secret Intelligence Service, also called MI6, participate in surveillance to obtain information for national security interests such as counter terrorism. Law enforcement agencies such as the United States’ Federal Bureau of Investigation (FBI) or the International Criminal Police Organization (INTERPOL) also perform surveillance. They concentrate on observing suspected criminals. Referred LINK