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

Nasdaq OMX Group said a problem with its global index data service was affecting index quote dissemination.

During the outage, traders said there were no quotes for the Nasdaq composite and the Nasdaq 100 index. Individual share price quotes were not affected, and trading volume in the first half-hour was the highest this week.

"There seems to be a data feed issue. It is making people hesitant to make decisions. A lot of traders base this index as sort of a sign post for trading. It's like someone just turned off the light," said Kevin Kruzenski, head of listed trading at KeyBanc Capital Markets in Cleveland.

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.

Nasdaq OMX shares were down 1.5 percent at $24.74.