Nasdaq on Thursday said it halted all trading - apparently the latest disruption to strike major exchanges and trading firms.

Nasdaq on Thursday said it halted all trading — apparently the latest disruption to strike major exchanges and trading firms.

The halt affected scores of big-name stocks, including Apple Inc. and Google Inc., leaving small investors and others scrambling to find out what’s happening in their portfolios.

The cause of the glitch was unknown, although Nasdaq put an alert on its website related to something known as its securities information processor, which disseminates stock quotes.

The Nasdaq options markets released an update recommending that all firms route their orders elsewhere.

All stocks listed on the New York Stock Exchange are trading normally, but trading in all Nasdaq-listed stocks and underlying options stopped early Thursday afternoon, according to Richard Adamonis, spokesman for NYSE Euronext.

“We are monitoring the situation and are in close contact with the exchanges,” SEC spokesman John Nester told the Los Angeles Times.

This is the latest in a series of technical problems that have struck stock markets and some big trading firms in recent years.

The most notorious was the so-called flash crash in 2010, in which the Dow Jones industrial average sank about 1,000 points in minutes, only to recover most of the loss minutes later.

The glitches have underscored what critics say is the fragility of the financial markets, despite the outward appearance of technological sophistication.

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(Los Angeles Times staff writers Andrew Tangel in New York and Jim Puzzanghera in Washington, D.C., contributed to this report.)

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