Nasdaq Blames Software Bug for Trading Outage

Lasted for three hours last week

Nasdaq OMX Group's (NDAQ.O) massive trading halt last week was due to a software bug and other internal technology issues triggered by problems at NYSE Euronext's (NYX.N) Arca exchange that led a key backup system to fail, the exchange operator said on Thursday.

Nasdaq said it was "deeply disappointed" by the three-hour outage on August 22, and while it pointed to connection problems between rival NYSE's electronic exchange Arca and the Nasdaq-run system that receives all traffic on quotes and orders for Nasdaq stocks, it took ultimate responsibility for the glitch.

"Our backup system did not work," Bob Greifeld, Nasdaq's chief executive, said in an interview.