(Reuters) - The software glitch that shuttered the Chicago Board Options Exchange for several hours on Thursday "cropped up unexpectedly," CBOE Holdings CEO Bill Brodsky told CNBC television on Friday.
The shutdown was the latest blow to confidence in the way U.S. financial markets operate. It prevented trading in options on two of the stock market's most closely watched indicators throughout Thursday morning.
Volume in index options was down by more than 12 percent from the day before as a result of the decline, as most trading was done in the afternoon.
Brodsky told CNBC that CBOE knows what the problem is, but would only describe it as an "internal issue." He said it was not related to a software upgrade.
On Thursday, more than 16.5 million contracts on single-stock equity options changed hands, more than the 15.6 million that traded Wednesday. CBOE, which normally accounts for 15 to 20 percent of daily volume, was responsible for just 3.2 percent of Thursday's market share, as activity shifted to other exchanges, according to OCC, formerly known as Options Clearing Corp.
Options on the Standard & Poor's 500, to which CBOE has the exclusive licensing rights, saw volume decline. Volume in S&P options fell 2.8 percent from Wednesday to Thursday, according to OCC data.
(Reporting by David Gaffen; Editing by Chizu Nomiyama; Editing by Chizu Nomiyama)