New York Stock Exchange Resumes Trading

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A trader outside the New York Stock Exchange on Wednesday. The exchange gave traders on the floor no warning before halting activity. Andrew Renneisen for The New York Times 
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.

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At 11:32 am, the exchange announced that it was shutting down all trading.
While the exchange said on Twitter that it decided to shut down trading to deal with the technical problems, it gave traders on the floor no warning before making the move.
“I was about to order my lunch and when I turned around the screens all went blank,” Mr. Costa said.
The shutdown was especially troubling because it came only hours after United Airlines temporarily grounded all of its flights following a technical issue. Other businesses had problems with their websites.
But both United and the New York Stock Exchange were adamant that the problems were a result of internal technical problems, rather than malicious hackers.
While there was no indication that the incidents were related, one prominent investor, Doug Kass, noted that the problems were a reminder that “in a paperless (and ‘cloudy’) world, investors and citizens are not likely as safe as the markets assume.”
The New York Stock Exchange, which is now owned by Intercontinental Exchange, has had, like other stock exchanges, technical difficulties in the past, but the scale of the problem on Wednesday has little precedent.
Other exchanges operated by the New York Stock Exchange, such as its options exchange, continued operating normally on Wednesday.
Federal regulators and law enforcement agencies are monitoring the situation but as of midday Wednesday there was no indication of anything malicious with the troubles at the N.Y.S.E., said several people briefed on the situation.
Mary Jo White, the chairwoman of the Securities and Exchange Commission, which oversees the nation’s securities markets, said in a statement, “We are in contact with N.Y.S.E. and are closely monitoring the situation and trading in N.Y.S.E.-listed stocks.”
President Obama was briefed on Wednesday about the New York Stock Exchange outage, a White House aide said, adding that officials there and at the Treasury Department were monitoring the situation.
Matthew Goldstein and Julie Hirschfeld Davis contributed reporting.