A three-hour trading outage on the Nasdaq last week was partly the result of issues within the company's control, the Nasdaq OMX Group said Thursday.
In a statement, the company detailed some of its early findings from an internal review. The Nasdaq blamed "a confluence of unprecedented events" that overwhelmed the exchange's system for handling price information. It said the catalyst was a torrent of messages from a trading platform run by the New York Stock Exchange, Arca.
"NASDAQ OMX is deeply disappointed in the events of August 22," the statement said, "and our performance is unacceptable to our members, issuers and the investing public."
The outage cracked the midday calm of a quiet summer day on Wall Street, sending brokers and traders scrambling to figure out what went wrong. Suspicion immediately fell on high-speed trading.
But on Thursday, the Nasdaq absolved high-speed trading of any blame. "Our review indicates that high frequency trading played no role in the technology events of August 22," the company's statement said.
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The trouble started in the morning, according to Nasdaq's version of events, when Arca tried to connect and disconnect more than 20 times with the Nasdaq's information processing system. Arca then sent a stream of price quotes for inaccurate stock symbols. The flood of data amounted to more than double the amount Nasdaq's processing system was tested to handle and 26 times the average flow. As a result, the company's processing system failed, which revealed a flaw in the system's software.
Shortly after noon, the Nasdaq sent out an alert that said it was stopping trading in shares listed on its exchange.
In its statement, the company said it had fixed the problem within 30 minutes but needed time to test its systems "to ensure that trading could be resumed in a fair and orderly manner."