The term "fifth column" typically describes a group that harbors secret sympathies for a cause despite outwardly appearing to believe in another. Typically, this "fifth column" works in a clandestine manner to undermine a particular group, while simultaneously voicing support for it to avoid suspicion. Fifth columns typically resort to espionage and disinformation as the primary weapons of their attacks.
The term "fifth column" finds its origins in a 1936 speech delivered by Spanish general Emilio Mola Vidal, in which he referred to a "fifth column" of support that would allow his forces to prove victorious during a forthcoming attack on Madrid. Common groups that currently are suspected of harboring fifth column tendencies are Arabs living within Israel, North Koreans living in Japan and right-wing paramilitary organizations within the United States.