"It makes it very difficult for people to invest in the market when they don't have a clue what a company's revenues and profits are," said Al Mirman, strategist at V Finance in Sarasota, Fla. "Companies are reporting profits that are not real. They are restating results. People just don't have confidence in companies."

The Dow closed down 215.46, or 2.2 percent, at 9,709.79, according to preliminary calucations. The last time the Dow finished lower was Feb. 7, when it stood at 9,625.44. The blue-chip index hasn't had a bigger one-day point drop since Feb. 4 when it lost 220.17.

Broader stock indicators also tumbled. The Nasdaq fell 53.17, or 3.3 percent, to 1,562.56. It was the Nasdaq's lowest close since Oct. 2.

The Standard & Poor's 500 index dropped 26.49, or 2.5 percent, to 1,040.65.

The sell-off accelerated in the final hour of trading, which analysts attributed to the Dow having broken below the 9,800 level and triggering programmed selling. Institutional investors often select a certain level at which to sell blocks of stocks.