NAB spokesperson George Wright confirmed an Australian report that KPMG would review how the error occurred.
"I can confirm that NAB has initiated a comprehensive investigation and review of the incident and all relevant matters associated with it. This independent review will be conducted by KPMG and will be provided directly to the CEO," Wright said.
The bank kept watch on whether forensic investigators have been called in for similar incidents or if KPMG will be addressing a specific incident.
Some 6500 customers have lodged compensation claims to seek refunds for fees and interest as of late last week, The Australianreported last week. It also reported the United Retail Federation would consider a class action against the bank for losses incurred by retailers for glitches in the bank's ATM and EFTPOS systems, and credit cards.
The outage is one of many to come, according to IBRS analyst Jorn Bettin who said that the problem big banks have is building new systems on top of outdated infrastructure.
"Banks are currently struggling with the issue of COBOL programmers going into retirement. The staff in question tend to be the last remaining experts in these languages and related technologies, and typically they are also the last remaining experts regarding specific — sometimes mission-critical — applications," Bettin said.