Trading on the New York Stock Exchange was shut down for hours on Wednesday as the exchange tried to cope with what appeared to be a technical glitch, rather than an attack.
It was the longest such suspension of trading at the exchange in recent years, although trading in the stocks listed on the N.Y.S.E. was able to continue on other stock exchanges, like Nasdaq.
Trading resumed late Wednesday afternoon, almost four hours after the shutdown began, less than an hour before the 4 p.m. closing bell.
When the shutdown began, Peter Costa, a trader on the floor with Empire Executions, said that exchange employees manually canceled about 700,000 orders that were in the system.
After canceling the orders, the exchange rebooted its systems, which was expected to take about 45 minutes.
The first technical problems appeared soon after the opening bell rang at 9:30 a.m. on Wednesday, when orders for several smaller stocks failed to go through, Mr. Costa and another trader on the floor said.
The initial issues only hit a small number of stocks, and the exchange appeared to have dealt with the problem, but they reappeared, on a more widespread basis, later in the morning, the traders said.