Nasdaq quotations for its main stock indexes resumed after nearly a one-hour outage as the market opened on Friday.

The Nasdaq OMX Group, whose shares slid 2.3 percent to $24.63, has not yet said what caused the problem, which affected index quote dissemination in its global index data service.

Several sector indexes finally displayed quotes, including the semiconductor index, about a half-hour after the main indexes resumed.

It could have thrown some monkey wrenches to the arbitrage guys ... if you're relying on the indexes for that, said Joe Saluzzi, co-manager of trading at Themis Trading in Chatham, New Jersey.

This is an interconnected market. everything links together, now more than ever, with all of the super computers out there. So if you take one chain off the link, it could cause problems, he said.

At Nasdaq's Times Square location in New York, the towering electronic screens gave no indication of the exchange's indexes some 45 minutes after the opening bell. Many of the screens instead showed quotes for the Dow Jones industrial average.

Also, during the outage, traders said they could not see quotes for the Nasdaq composite and the Nasdaq 100 index. Individual share price quotes were not affected, however, and trading volume in the first half-hour was the highest this week.

Nasdaq OMX said the data on World Currency Options, ETFs, the KBW bank index, the Russell 2000, and other indexes were not affected by the outage.

The Nasdaq said its options market would review trades in options of the Nasdaq-100 because of the index price feed problems at the opening.

(Reporting by Caroline Valetkevitch, additional reporting by Angela Moon and Jonathan Spicer; Editing by Padraic Cassidy)