The chief executive of the Nasdaq stock exchange, Robert Greifeld, on Friday shot back at criticism of how his exchange handled a three-hour halt in trading on Thursday afternoon.
Mr. Greifeld said in an interview on Friday morning that the breakdown on Thursday had been set off by another participant in the market, not something inside Nasdaq.
“We had an external environment happen,†he said.
That problem, which Mr. Greifeld declined to describe more fully, caused issues with the data system that provides prices for recent trades in Nasdaq stocks. Nasdaq operates that system.
The long-time Nasdaq executive said that the exchange needs to work on its “defensive driving†to deal better with mistakes by others.
The exchange was up and running smoothly on Friday morning, and the Nasdaq composite index was trading up slightly. But the exchange has heard from angry customers and industry veterans who said that the company left the market in confusion for much of the lengthy shutdown, during which none of the stocks listed on Nasdaq could be bought or sold.
Mr. Greifeld said that he did not understand the criticism.
“In our opinion, we communicated with our constituents as well as we possibly could have,†he said.
The incident happened less than two years after a problem with Nasdaq’s technology delayed the initial public offering of Facebook stock. Mr. Greifeld said that the two big incidents don’t point to any deeper flaw with Nasdaq’s technology system.
“People recognize the superior nature of our technology,†he said. “We recognize that we need to get better at what I’m calling defensive driving. â€
Nasdaq’s own stock was up 1.2 percent on Friday morning, after falling 3.4 percent on Thursday.
