SINGAPORE - A software failure and subsequent human oversight were behind the major disruption in OCBC Bank's services for about three hours last Saturday (Sept 1).
Chief executive Samuel Tsien said on Tuesday (Sept 4) that there was a problem in "the back-up unit for the core banking system", which meant customer transaction data was not transferred.
The glitch, which has prompted a response from the regulator, caused the core banking system's storage to reach maximum capacity. This, in turn, stopped it from accepting new data, he added.
Mr Tsien added: "The software failure was, unfortunately, not detected for rectification due to a human oversight."
The problem affected OCBC's ATM network, online banking channels, Nets and card services from about 8.45pm last Saturday. They were gradually restored after 11.30pm.
Mr Tsien added in an e-mail statement: "As we restarted the system to restore the services, we made sure that all customer and transaction data was protected."
He added that the service disruption was "totally unacceptable" and that measures had been put in place to prevent a recurrence.
The outage drew complaints from users on social media sites, with customers citing problems ranging from cash withdrawals to getting online access to their accounts.
A spokesman for the Monetary Authority of Singapore (MAS) said OCBC notified it last Saturday that it was encountering intermittent disruption to its provision of Internet banking, ATM, Fast and card payment acceptance services to customers.
"We have instructed OCBC to identify and address the root causes of the disruption, and submit a thorough investigation report," the spokesman added.
It also said that it will closely monitor OCBC's rectification measures following the service outage, and where necessary, take appropriate supervisory actions.
The MAS said critical IT systems are required to be tested regularly to ensure that they can resume operations within four hours following any disruption, and to have a maximum unscheduled downtime of no more than four hours across a 12-month period.