"Initially, it was thought he was running a simple pyramid scheme. But Steve Harbeck, head of the Securities Investor Protection Corporation and the receiver of Madoff's broker-dealer business, said the investigation had uncovered a trove of records stretching back at least 20 years. "We do not seem to be dealing with a traditional Ponzi scheme alone," said Harbeck. "Ponzi" frauds occur when the money from new investors is used to pay existing ones. "This seems to be something of a hybrid," Harbeck said, adding that the potential losses could be far greater than anyone first thought."