Black Helicopters (BH) are not just helicopters with a black paint-job as you may have been told. They are, in fact, autonomous agents -- lifeforms -- created by New World Order (NWO) agencies via nanobiotechnology. Their primary purpose is to spy on the activities of average citizens in order to gather tactical information and discover "subversives" who are not bowing to the will of the Liberati's UN-backed Federal Government. Furthermore, when the NWO Invasion takes place in the not-too-distant future, they will round up citizens for internment in concentration camps or carry out the elimination of the more vocally anti-Liberati.
This page tickles my conspiracy theory funny-bone in almost every conceivable way. This page will arm you with all the information you need to know about Black Helicopters in order to convince anyone that you are completely nuts.
It's even got posters you can print out and hang up: "The Nanobiotechnological Menace of Black Helicopters (PDF)"