A mysterious glitch halted trading on the Nasdaq for three hours on Thursday in the latest major electronic breakdown on Wall Street, embarrassing the stock exchange that hosts the biggest names in technology, including Apple, Microsoft and Google.
The problem sent brokers racing to figure out what went wrong and raised new questions about the pitfalls of the electronic trading systems that have come to dominate the nation's stock markets.
Nasdaq only said that the problem lay in its system for disseminating prices and that it planned to investigate.
The outage disrupted what had otherwise been a quiet summer day on Wall Street. It was another in a series of technical problems to disrupt financial markets in recent years, though less alarming than the "flash crash" plunge of May 2010.
The Nasdaq, an exchange dominated by some of the largest, most prosperous technology companies, sent out an alert shortly after noon that said trading would stop. The Nasdaq composite index spent much of the afternoon stuck at 3,631.17.
Trading resumed at 3.25 pm. Thirty-five minutes later, the day ended with the index up 38 points, or 1 per cent, at 3,638.71.
Investors were not at risk of losing any money from this type of glitch, said Marty Leclerc at Barrack Yard, chief investment officer at Barrack Yard Advisors. "Clearly it's an annoyance, but it doesn't in any way affect the value of your underlying assets," Leclerc said. "Warren Buffet used to say that if you own a stock, you ought to be comfortable with it even if the market were to close for a year."
During the outage, the Nasdaq said it would not cancel any orders stuck in limbo, but that customers were free to cancel them.
The stock of the exchange's parent company, Nasdaq OMX, took a hit, falling $1.08, or 3.4 per cent, to close at $30.46 in heavy trading.
The White House, the Treasury Department and other government agencies monitored the disruption.
Thursday's shutdown was another sign that the days of stock brokers in colorful jackets roaming the floor of the stock exchange have faded away. Now powerful computer programs dominate trading by sifting through reams of data and executing trades in fractions of a second. That makes trading faster and, arguably, more efficient. But it also introduces more possibilities for errors that can jolt the entire market.
Last year, BATS Global Markets tried to go public on its own exchange but had to back out after a computer error sent its stock price plunging to just pennies. Nasdaq
mishandled Facebook's public offering last spring, when technical problems kept many investors from knowing if their trades had gone through and left some holding unwanted shares. And in April, the Chicago Board Options Exchange shut down for a morning because of a software problem.
Then there was the 2010 "flash crash" in which the Dow Jones industrial average fell hundreds of points in minutes before eventually closing 348 points lower. It was one of the first major problems that revealed to the public the potential dangers of computerized trading.
PHOTO: Associated Press 
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