Update 3:28 p.m.: Trading has resumed on Nasdaq following three-hour outage caused by a technical glitch.
Nasdaq halted trading Thursday because of a technical problem, the latest glitch to affect the stock market.
The exchange sent out an alert to traders at 12:14 p.m. Eastern saying that trading was being halted until further notice because of problems with a quote dissemination system. More than an hour later, trading was still halted.
The glitch was the latest incident to raise questions about the dangers of trading via machine, following a sudden plunge in stocks in May 2010 that came to be known as the "flash crash" and the glitch-plagued initial public offering of Facebook last year.
Nasdaq said it wouldn't be canceling any open orders, but that customers could cancel orders if they wanted to.
Nasdaq sent out an update at 1 p.m. EDT saying trading would reopen "at a time to be determined."
The Nasdaq composite index was frozen at 3,631.17, up 31.38 for the day. The index is up 20 percent so far this year.
Securities and Exchange Commission spokesman John Nester said: "We are monitoring the situation and are in close contact with the exchanges."
- Hear the earlier interview with Marilyn Geewax, NPR senior business editor, at 1:35 p.m. Eastern.
This segment aired on August 22, 2013.