And why does it have so many believers?
Illminati means "the enlightened ones". It is the name of an ancient brotherhood. In the 1500 s, a group of some of Italy's most enlightened men- physicists, mathematicians, astronomers- began meeting secretly to share their concerns about the church's inaccurate teachins. They feared that the church's monopoly on "truth" threatened academic enlightenment around the world. They founded the world's first scientific think tank, calling themselves "the enlightened ones"- the Illuminati. The Illuminati were hunted ruthlessly by the Catholic Church and only through rites of extreme secrecy did the scientists remain safe. The scientists met regularly in Rome at an ultrasecret lair they called the "Church of Illumination" --- all this infromation was from a book called "Angels and Demons" by Dan Brown. It deals with a lot about the Illuminati.
The Illuminati (plural of Latin illuminatus, "enlightened") is a name given to several groups, both real (historical) and fictitious. Historically the name refers to the Bavarian Illuminati, an Enlightenment-era secret society founded on May 1, 1776. In more modern contexts the name refers to a purported conspiratorial organization which is alleged to mastermind events and control world affairs through governments and corporations to establish a New World Order. In this context the Illuminati are usually represented as a modern version or continuation of the Bavarian Illuminati.
Illuminati was an old group of enlightened people. Now, conspiracy theorists are using them as a crutch to scare and disturb the masses and earn an income out of it. IT's like the marketers who spread the '2012 21st december doomsday' hype. The masses just believe what they hear and find fascinating. --- IT's just a dumb little over the top unrealistic story basically.