okay, not so simple.
lonely girl and the war of the worlds broadcast (which actually was not a hoax, or not intended to be anyway) -- both "worked" because of the way they used new media.
sometimes hoaxes do not "undo" but rather create a climate of fear. "what if I do something and someone mocks it." sincerity is always risky. the hoax inherently protects the provocateur because they're "in." sometimes the hoax is annoying and boring. sometimes it is mean and dangerous.
the hoax is a form.