Nasdaq admits partial responsibility for a three-hour freeze in trading on the tech stock exchange last week.
Nasdaq OMX also pointed the finger at NYSE Euronext, blaming it for overwhelming Nasdaq's systems.
The NYSE's Arca system sent "a stream of inaccurate symbols" on 22 August and cut out over 20 times, swamping Nasdaq's computers.
"Our backup system did not work" Nasdaq chief executive Bob Greifeld said in an interview. "There was a bug in the system ... and we need to work hard to make sure it doesn't happen again."
The glitch was fixed within 30 minutes, but the BBC reports testing took three hours to complete before the market could open again.
