(Bloomberg News) A crackdown on investment frauds including Ponzi schemes and stock market manipulation resulted in U.S. enforcement action against 343 criminal defendants and 189 civil defendants since August, the Justice Department said.

The criminal cases alone involved more than $8.3 billion in estimated losses and more than 120,000 victims nationwide, Attorney General Eric Holder said at a news conference in Washington today.

"All of these victims can tell a tragic and cautionary story of being misled and exploited -- often by someone they trusted," Holder said. "Many of the scam artists we've identified were preying on their own neighbors -- and on the most vulnerable members of their communities."

The crackdown was organized by the Obama administration's multiagency Financial Fraud Enforcement Task Force, created a year ago after the U.S. recession led to an increase in economic crimes. The law enforcement operation is the first of its kind to target a wide range of schemes that prey on investors, according to the Justice Department.

Cases include a man who pleaded guilty in Texas for his role in an oil and gas investment Ponzi scheme defrauding 7,700 investors of more than $485 million. In a case in Florida, a defendant was convicted for an investment scam that targeted the Haitian community.

Fraud Schemes Increasing

As more people turn to third parties to manage their money, the frequency of the investment schemes rises, said Robert Khuzami, director of the Securities and Exchange Commission's enforcement division, at the news conference.

The criminal cases resulted in 64 arrests, according to the Justice Department.

The Justice Department enforcement numbers also include indictments, convictions and sentencings. In some cases the same defendants faced civil and criminal enforcement actions, according to the Justice Department.

In a Ponzi scheme, money from the newest investors is used to fund the returns that have been promised to previous investors.