Every NASDAQ-listed stock – Apple, Facebook, Microsoft, etc. – was halted. As a result, both the index and individual stocks flatlined.
The exchange just re-opened for trading at 3:25 PM ET.
Options trading will resume at 3:35.
NASDAQ said the trading halt was due to a UTP SIP quote dissemination issue.
(UTP stands for "unlisted trading privileges" and refers to the ability of other exchanges to trade securities listed on the NASDAQ. SIP stands for "securities information processor" and is the system that allows NASDAQ to send quotes for those securities to other exchanges.)
More to come...