Thomson ReutersA trader waits for news while working on the floor of the New York Stock Exchange following a halt in trading in New York

WASHINGTON (Reuters) – When the New York Stock Exchange came to a surprise standstill of more than three hours on July 8, trading simply migrated to other exchanges, according to an analysis released by the U.S. Securities and Exchange Commission on Wednesday.

Trading halted at 11:32 a.m., raising fears that one of the world’s largest stock exchanges had fallen prey to a cyber attack. Officials said a technical glitch caused the three-hour, 38-minute break.

In looking into the event, the SEC, the top U.S. securities regulator, found “total trading volume in NYSE-listed corporate stocks on July 8 was well within the range of observed trading volume in the first seven months of 2015.”

“While the NYSE’s share of trading volume declined, other market centers – especially other exchanges – experienced unusually large increases in trading volume in NYSE-listed stocks on July 8,” it said, adding that NASDAQ took on a large portion of trading.

The Arca, BATS-Z and Edge-X exchanges attracted trades, as well.

The SEC does not plan any follow-up analyses or research on the events of July 8.

The NYSE, a unit of Intercontinental Exchange Inc , accounts for more than 60 percent of SP 500 volume at the close of the market. Nearly all U.S. trading is done electronically and the NYSE outage again raised questions about the robustness of the technology at exchanges after a raft of major glitches in recent years.

The unexpected closure had an effect on spreads and depths, two metrics of liquidity, the SEC found. It had the greatest impact on smaller and less actively traded NYSE stocks’ spreads, it said.

“Quoted spreads for NYSE-listed stocks increased immediately prior to the suspension of trading and remained elevated for the next 75 minutes,” it said.

The spreads only shrank after trading resumed on NYSE.

Meanwhile, inside dollar depth declined, the SEC said.

(Reporting by Lisa Lambert; Editing by Bill Trott)

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