NEW YORK -- Federal authorities, responding to the subprime-mortgage crisis, have formed a task force to determine if lenders or Wall Street firms participated in fraud.

The $330-billion auction-rate securities market will "cease to exist" after it collapsed in February because Wall Street firms stopped using their own capital to buy bonds when demand fell short, a Citigroup Inc. analyst said.

Highly unusual intervention may put central bank's resources to the test The Federal Reserve's extraordinary move to rescue a tanking investment giant and expand its emergency lending appeared to pay off Monday. Although most U.S. markets showed fresh signs of strain, none snapped, and while some banks and Wall Street firms saw their stocks pummeled, none collapsed.

Many college students across the nation will begin to see higher costs for loans this spring, while others will be turned away by banks altogether as the credit crisis roiling the U.S. economy spreads into yet another sector, student lenders and Wall Street firms say.

-- State regulators and cities that have filed cases or disclosed investigations targeting Wall Street firms' roles in the subprime mortgage market:

The plan, hammered out after weeks of talks among Treasury officials, mortgage lenders and Wall Street firms, would allow distressed borrowers who are current on their payments to keep their low introductory rates.