In separate arrests, two former Bear Stearns managers in New York were indicted Thursday, becoming the first executives to face criminal charges related to the collapse of the subprime mortgage market.

Mortgage foreclosure rescue scams, which promise to help struggling homeowners stave off foreclosure and keep their homes, also have become a major problem, officials said. Typically, unsuspecting owners sign over their homes and then find they are victims of fraud.

Officials declined to say who might be the next corporate target, but Mueller said the investigations focus on accounting fraud, insider trading, and failure to disclose the value of mortgage-related securities and other investments.

Under review for potential fraud are: investment banks, hedge funds, credit rating agencies, brokerage houses and due diligence firms - which evaluate loans packaged into investments.