Well, here is a first hypothesis, which ought to freak out any Robert Anton Wilson fan: Mohammed Atta was a fan of Illuminatus, and took some inspiration from the terrorists in the book. As the article on the Egyptian New Year, linked above, testifies, there is a great appetite in the Muslim world for elaborate conspiracy theory involving esoteric secret societies. The constitution of Hamas is a good example, in the way it groups Rotary Clubs and Freemasons together as part of the grand anti-Islamic conspiracy. And Illuminatus!, while largely unknown to the literary mainstream, is well-known to conspiracy aficionados of all sorts. For that matter, Atta spent a lot of time in Germany, where Illuminatus! had already intersected real espionage in the person of "Hagbard Celine", a young hacker who took his name from one of the novel's anarchist heroes, and who penetrated Western computer networks on behalf of the KGB.
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