The Fifth Power (O 5º Poder) (1962)

Foreign country wants to perpetrate a "coup" in Brazil. They employ a new technique of subliminal messages, which are transported along with radio and TV waves. In no time, the population gets deranged and the country dives into ultimate chaos. Only a few people who don't watch television nor listen to radio are immune to it, and have the responsibility to abort the scheme, without really knowing what they're dealing with.