Trading in Nasdaq-listed securities has resumed after being halted for several hours because of a technical problem in distributing stock price quotes.
All traffic through Nasdaq stopped at 12:14pm EDT (16:14 GMT), the exchange said on its website on Thursday. It resumed nearly three hours after trading in Apple, Google, Microsoft and more than 3,000 other US companies had been abruptly halted.
"Any brokerage firm gets paid by executing orders," said Sal Arnuk, co-head of equity trading at Themis Trading in Chatham, New Jersey. "So yes, we are frustrated, and this hurts us, it hurts the market and it hurts public confidence."
A source familiar with the matter described the problem as a "data feed issue".
Earlier, rival exchanges, including NYSE Euronext's New York Stock Exchange, had halted trading in Nasdaq-listed shares.
Trading of shares not listed on Nasdaq continued, but transactions could not be executed on the Nasdaq platform. Options trading was also halted.
'Level of automation'
Nasdaq is the second-largest US stock exchange operator. In all, it lists about 3,200 shares.
"I can't remember this happening in recent memory," said Christopher Nagy, president of consultancy firm KOR Trading and a former head of trading at TD Ameritrade.
Before the halt, the Nasdaq Composite Index had been up 0.87 percent.
Thursday's outage was the latest of a flurry of high-profile glitches that have become familiar to participants in US stock markets.
"As we continue to eliminate human beings from the execution of security trading, this is the problem you run into," said Stephen Massocca, managing director of Wedbush Equity Management LLC in San Francisco. "These events are going to take place, given the level of automation."
On Tuesday, a technical problem at Goldman Sachs Group Inc resulted in a flood of erroneous orders being sent to US equity options markets.
Two weeks earlier, on August 6, stock exchange operator BATS Global Markets was hit with a nearly hour-long outage.