Loyalty oaths
From dKosopedia
In the 1950s, demands were frequently placed on suspected leftists and other "unreliable" citizens that they sign Loyalty oaths. Since those who insisted that citizens sign these loyalty oaths to give assurance that they would not betray their own country were surely aware that a moderately well-trained foreign agent would swear to anything that would help him do his job more effectively, other of their goals must have been served by the making of these demands.