What is the hypodermic needle theory all about?

It's an outdated theory of communication that suggests that an audience is helpless to the effects and messages of a medium, such as television. The theory says that an audience will absorb all of the intended information; they will unknowingly believe anything they see. This theory was very popular in the 1930s, especially after H.G. Wells' "War of the Worlds" broadcast in 1938, but has since been disproven by more modern theories.