Madoff Charged in $50 Billion Fraud at Advisory Firm

Bernard Madoff, founder and president of a New York firm that invested funds for wealthy individuals, hedge funds and other institutions, was charged with operating what he told employees was a long-running $50 billion Ponzi scheme in what may be one of the largest frauds in history.

from Wikipedia:

A Ponzi scheme usually offers abnormally high short-term returns in order to entice new investors. The perpetuation of the high returns that a Ponzi scheme advertises (and pays) requires an ever-increasing flow of money from investors in order to keep the scheme going.

The system is destined to collapse because there are little or no underlying earnings from the money received by the promoter. However, the scheme is often interrupted by legal authorities before it collapses, because a Ponzi scheme is suspected and/or because the promoter is selling unregistered securities. As more investors become involved, the likelihood of the scheme coming to the attention of authorities increases.