The story goes that in 1785 (or possible late 1784) an Illuminati messenger (and initiate, according to some) named Lanz was struck and killed by lightning outside Regensberg while on his way to France. He was carrying plans for a revolution, detailed by a German writer named Xavier Zwack. The police found the documents on his body and turned it over to the government, which led to police raids of Illuminati lodges and the homes of some of its members. The organization was outlawed and broken up in 1785.

There's no way to be certain of this however, just like it's virtually impossible to verify anything about the Illuminati. This is not because there's a a sinister plot to cover things up but because so much crap has been written about it that the signal-to-noise ratio is incredibly low. Almost anyone who writes about the Illuminati has a political agenda of his own to promote, and most authors end up citing other, equally biased authors, as credible sources.

For example, many people point out that the aim of the Illuminati was the destruction of all kings and religion (except the Jewish) and total control over the masses. This sounds a lot like the Protocols of the Elders of Zion to me (for those who don't know of the Protocols, they were supposed to be evidence of an International Jewish Conspiracy, published in the late 19th century), in that the Zwack papers were used to discredit the Illuminati in much the same way as the Protocols were used to discredit the jews. Also, manu people point out that the French Revolution indeed happened exactly like Weishaupt predicted. To me, that just means that the plans credited to Weishaupt were written after the revolution actually took place.