Westpac is currently investigating the cause behind why customers were unable to access their online or mobile banking for six hours on Monday.
A Westpac spokesperson said the issue occurred following scheduled updates that were made to its Westpac Live platform.
"We are thoroughly investigating the matter," the spokesperson told ZDNet.
"This is not the standard of service we aim to provide our customers and we're sorry for the inconvenience caused."
The spokesperson confirmed Westpac's mobile and internet banking is, however, now back up and running, following the "system issue".
Westpac first acknowledged the issue in a tweet at 9:50am AEST, with the bank saying it was experiencing "intermittent issues" with Westpac Live Online and Mobile Banking.
"We're working to fix these ASAP," the bank stated.
It informed frustrated customers that its IT teams were working to resolve the glitch.
The bank, however, assured customers that ATMs, Eftpos, branch services, telephone banking, and Bank@Post were still operating as normal.
This glitch comes just as the bank is about to say goodbye to group CIO Craig Bright, who officially finishes up with the company on September 25.
In July, the red and white bank announced it standing up a new group operating office that will combine the functions of its existing group operations and group technology arms.
Leading the division as its chief operating officer will be Scott Collary, who will join Westpac from Bank of Montreal in Canada where he held the role of chief information and operations officer for its North American personal and business banking, private wealth, and global asset management divisions.
COO Gary Thursby, who has also resigned and is due to leave Westpac early next year, will act as CIO until Collaroy's employment commences later this year.
Westpac in June said "a mix of technology and human error" and "deficient financial crime processes" were to blame for its failure to comply with anti-money laundering obligations.
The anti-money laundering and terrorism financing regulator applied to the Federal Court of Australia alleging Westpac was involved in "systemic non-compliance" with the Anti-Money Laundering and Counter-Terrorism Financing Act 2006 (AML/CTF Act) on over 23 million occasions.
Specifically, Austrac said the bank had consistently failed to: Assess and monitor ongoing money laundering and terrorism financing risks; report over 19.5 million International Funds Transfer Instructions (IFTIs) to Austrac over nearly five years for transfers both into and out of Australia; pass on information about the source of funds to other banks in the transfer chain; keep records relating to the origin of some of these international funds transfers; and carry out appropriate customer due diligence on transactions in the Philippines and South East Asia that were related to potential child exploitation risks.
Updated 7 September 2020, 4:18pm AEST: Additional details and Westpac comments added.
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