A fifth column:Wiki

A fifth column is a group of people who clandestinely undermine a larger group, such as a nation, from within. A fifth column can be a group of secret sympathizers of an enemy that are involved in sabotage within military defense lines, or a country's borders.^[1] A key tactic of the fifth column is the secret introduction of supporters into the whole fabric of the entity under attack.^[2] This clandestine infiltration is especially effective with positions concerning national policy and defense.^[2] From influential positions like these, fifth column tactics can be effectively utilized, from stoking fears through misinformation campaigns, to traditional techniques like espionage.^[2]