NEW YORK (CNNMoney.com) -- It remains perhaps the most striking act of guerrilla theater in American history, certainly in the financial world.

On a steamy summer morning forty years ago - Aug. 24, 1967 - about a dozen young men and women led by James Fourrat and Abbie Hoffman entered the visitors' entrance to the New York Stock Exchange at 20 Broad Street. (The trading floor gallery had been open to visitors since 1939.) They waited while a member of the security staff approached; the group had previously phoned the exchange and asked for a tour, but the guards became nervous about the way that some in the group were dressed.

Still, the group went up to the visitors' gallery, two stories above the busy trading floor. They snaked their way past exhibits showing the virtues of the industrial revolution and the development of modern capitalism. As they turned the corner, they encountered a horde of reporters and cameras.

This made exchange officials nervous. John Whighton, the captain of the exchange's security force, told the group that no demonstration of any kind would be tolerated. Whighton asked the group for a name, and Fourrat said: "George Metesky," and identified his group as ESSO, the East Side Service Organization (the first a reference to New York's "Mad Bomber" from the 1950s, the second to the successor to Rockefeller's Standard Oil). The guard wrote "George Metesky and friends" on a pad, and escorted the group up to the railing directly above the trading floor.

Immediately, the group of pranksters began throwing handfuls of one-dollar bills over the railing, laughing the entire time. (The exact number of bills is a matter of dispute; Hoffman later wrote that it was 300, while others said no more than 30 or 40 were thrown.)

Some of the brokers, clerks and stock runners below laughed and waved; others jeered angrily and shook their fists. The bills barely had time to land on the ground before guards began removing the group from the building, but news photos had been taken and the Stock Exchange "happening" quickly slid into iconic status.

Once outside, the activists formed a circle, holding hands and chanting "Free! Free!" At one point, Hoffman stood in the center of the circle and lit the edge of a $5 bill while grinning madly, but an NYSE runner grabbed it from him, stamped on it, and said: "You're disgusting."

If the prank accomplished nothing else, it helped cement Hoffman's reputation as one of America's most outlandish and creative protestors. Along with Jerry Rubin and others, Hoffman had founded the Youth International Party earlier that year, and the "Yippie" movement quickly became a prominent part of America's counterculture.

The event was not the first political assault on Wall Street, and certainly not the most violent. At noon on Sept. 16, 1920, a bomb in a horse-drawn carriage exploded near the Wall Street office of J.P. Morgan & Co., ultimately killing 38 people and wounding hundreds. Trading at the NYSE stopped for the rest of the day; although no one was ever charged with the crime, authorities suspected Italian anarchists as having been responsible.

The Yippie prank obviously had less impact. Don Charles, a photographer who shot the event for The New York Times, today has no particular recollection of the event, and says that in his mind, the Yippie demonstrations at the following year's Democratic convention in Chicago stood out more.

Still, Hoffman would later boast of his NYSE exploit: "In the minds of millions of teenagers the stock market had just crashed."

Perhaps. Although Hoffman was speaking largely of a symbolic crash, the Dow Jones industrial average did in fact finish that week down 24.97 points, at 894.07. And in 1967 the market began one of the most sustained bear periods in its history.

Of course, no one would attribute that bear market directly to the Yippies' intervention. The U.S. economy began to suffer under the weight of spending on the Vietnam War and Great Society programs, and the stock market's lackluster performance reflected that economic stagnation.

The event did appear to have one direct effect: officials moved to insure that nothing like it could occur again. Some three months later, the NYSE installed bulletproof glass panels, 1-3/16 inches thick, around the visitors' gallery, as well as a metal grillwork ceiling. An exchange spokesman told the New York Times at the time that it was for "reasons of security."