ASX boss Dominic Stevens has apologised for the "unacceptable" outage that stopped trading on the Australian stock market on Monday but defended its handling of the situation.
A report by the exchange operator into the outage has revealed the trading chaos was caused by an unprecedented hardware malfunction that resulted in the trading system not properly connecting to a backup database at the ASX disaster recovery site, or DRS.
The fault forced the ASX to delay the opening of trade by 90 minutes till 1130 AEST and close at 1405 AEST after a session where not all parts of the market were able to trade.
Mr Stevens said the outage was "especially disappointing" because the ASX had a record of reliability, with no failures in seven of the past 10 years and 99.7 per cent reliability in those years where problems did occur.
"The outage to ASX Trade last Monday was unacceptable to the market and unacceptable to ASX. I again offer my apologies for the disruption caused," he said.
Friday's report states there was a "degradation and ultimately failure" of the database supporting the ASX Trade trading system at 0657 AEST on Monday, and the "fail-over" to the backup DRS database did not occur fully.
While problems were detected and the delayed opening took place, subsequent problems occured with trades not being executed correctly.
A block of trades around 1110 AEST were later cancelled as invalid.
The report said the ASX and its vendors have not encountered a fault of this nature before but have now put procedures in place to deal with it if it happens again.
Mr Stevens defended the decision to end trade early.
"ASX does not decide to close the market lightly," he said.
"Understandably, concerns have been raised on various fronts. However, we make no apologies for following our long-established and well-understood protocols nor for exercising our judgement to ensure the market was fair, orderly and transparent."
Mr Stevens also confirmed ASX was cooperating with a review of the outage by the Australian Securities and Investments Commission.
