The Fifth Column is a reference to the TV series V.
Older than that, it is a reference to the media. The “Fourth Estate or Fifth Column, Dis-informers” is an old term to describe how the media tries to become a column of government through disinformation and manipulating the other levels of government and society. The origin of the term Fifth Column came from Spain where General Mola claimed to have supporters fighting in Madrid while he was leading four columns of his army to invade the city during the Spanish Civil War.