A nationwide law enforcement crackdown targeting financial fraud has led to cases against 343 criminal defendants involving $8.3 billion in estimated losses, Attorney General Eric Holder announced Monday.

"Operation Broken Trust" is the first national effort of its kind aimed at a broad array of investment fraud schemes and the 3 1/2-month campaign was organized by the Obama administration's Financial Fraud Enforcement Task Force.

The schemes that were uncovered highlight "the pervasiveness of the threat," Shawn Henry, the FBI's executive assistant director, told a news conference.

In one case in Texas, an oil and gas investment Ponzi scheme defrauded 7,700 investors of more than $485 million. In another case, in Chicago, the operator of a Ponzi scheme victimized elderly Italian immigrants and hundreds of others after promising them annual returns of 10 to 15 percent.

Seventy-five investors lost $89 million in a Ponzi scheme in Florida. Nevin Shapiro, who pleaded guilty for his role in the scheme, used some of the money to pay illegal sports gambling debts, to buy floor seats at Miami Heat basketball games and to make payments on his yacht and his residence in Miami Beach.

Two Florida-based hedge fund managers, Bruce Prevost and David Harrold, were accused by the Securities and Exchange Commission of fraudulently putting more than a billion dollars' of investors' money in a Ponzi scheme operated by Minnesota businessman Thomas Petters. The SEC says that when Petters was unable to make payments, Prevost and Harrold concealed it from investors.

Yet another Ponzi scheme targeted members of the Haitian community in Florida, claiming 500 victims who lost $14 million after being promised that they would double their money in 90 days. A participant in the scheme, Ronnie Bass Jr., was convicted in federal court in October.

The law enforcement operation is a warning that cheating investors out of their earnings and savings "is no longer a safe business plan," said Holder.

In addition to the criminal cases arising from the probe, civil cases involved estimated losses of more than $2.1 billion.

In all, the schemes harmed more than 120,000 victims. Eighty-seven defendants have been sentenced to prison. There were 231 criminal cases and 60 civil enforcement actions.