The Australian Stock Exchange says it expects to open as usual at 10am AEST this morning after it was offline most of yesterday.
Some on social media were quick to speculate the bourse had been hit by a cyber-attack, such as the DDoS effort that took the NZX offline for the best part of a week during August.
But ASX chief executive Dominic Stevens said it was in fact a software upgrade gone awry - despite a year of testing and four dress rehearsals.
Monday saw a new version of the ASX Trade equity platform debut - only to fall over just 30 minutes after the market opened.
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ASX Trade was developed by Nasdaq, which could not resolve the problem on Monday. But the US exchange, working with "specialist third parties," was confident it would be fixed overnight. The glitch hit combination trades, or those involving multiple stocks.
But Stevens said the buck stopped with the ASX.
"The outage falls short of the high standards we set ourselves and the standards others expect of us," the CEO said in a statement.
"Notwithstanding the extensive testing and rehearsals, and the involvement of our technology provider, ASX accepts responsibility. The obligation to get this right and provide a reliable and resilient trading system for the market rests with us."
Meanwhile, the Australian Securities and Investments Commission says it holds "significant concern" following the ASX's outage on Monday, saying it had a "significant impact on the market".
"Following the reopening of the market, ASIC will determine whether ASX followed the relevant regulatory requirements under the Corporations Act and met its obligations under its Australian Market Licence," the regulator said in a statement.
"In addition to ASIC's expectations that this outage will be resolved as soon as is possible in a safe manner, ASX will be required to provide a full incident report to ASIC."