NEW YORK - A computerized sell-off, possibly caused by a typographical error, triggered one of the most turbulent days in Wall Street history Thursday and sent the Dow Jones industrial average to a loss of almost 1,000 points, nearly a tenth of its value, in less than half an hour.
It was the biggest drop ever during a trading day.
The Dow recovered two-thirds of the loss before the closing bell, but that was still the biggest point loss since February of last year. And even with the partial recovery at the close, the decline cost investors $462 billion, based on the Dow Jones U.S. Total Market Index.
The lightning-fast fall temporarily knocked normally stable stocks such as Procter & Gamble Co. to a tiny fraction of their former value and sent chills down investors' spines. In a span of two seconds Thursday shares of Radian Group Inc., a Center City mortgage insurer, plunged from $8.38 to a penny and then back again to $8.38.
On the trading floor of the New York Stock Exchange, traders shouted or watched open-mouthed as the screens lit up with prices plummeting and as phones rang off the hook. In Philadelphia, Theodore R. Aronson of Aronson, Johnson & Ortiz L.P., a money-management firm with $20 billion in assets, said: "It was almost like 'The Twilight Zone.' "
