The International Securities Exchange (ISE) had to suspend trading last Friday (12 October 2007) following a power outage.
The problem at the ISE's New Jersey site resulted in the temporary suspension of trading in both the options and stock exchanges at 10.16am.
The ISE was able to re-open the stock exchange at 11.30am, and the options exchange at 12.00pm.
The ISE said, "The ISE has undertaken a thorough review of the cause of the issue, and will take all necessary steps to prevent a recurrence."
It did not release any further details about the exact cause of the outage. Mission critical systems like stock exchanges normally have back-up power sources.