They took advantage of the trading floor gallery being open to visitors since 1939. They scheduled a tour prior to their arrival.
In spite of initial reservations by security personnel, they signed in as "George MEtesky" and friends, after Fourrat identified himself as George Metesky (a/k/a the Mad Bomber who set a series of bombings throught New York City in the 1940s and 1950s) and the group as ESSO, the East Side Servicce Organization (A play on Rockefeller's Standor Oil), the guards led the group to the railing overlooking the trading floor.
Upon arriving at the overlook, the group immediately began throwing fistfulls of dollar bills onto the trading floor. The exact amount thrown was estimated between 30 and 300.
The group was immediately escorted out of the building, at which point, the group formed a circle, while Hoffman lit the edge of a $5 bill as he stood in the middle.
While the prank did not have substantial impact, on the exchange, trading was not even suspended.
The only real result: NYSE installed bulletproof glass panels around the visitors' gallery, with a metal grill ceiling, for "reasons of security" three months later.