Nasdaq has halted trading because of a technical problem.
The exchange sent out an alert to traders saying that trading was being halted until further notice because of problems with a quote dissemination system.
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. saying trading would reopen "at a time to be determined."
The Nasdaq composite index was frozen at 3,631.17 as of 1:20 p.m., 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."