Westpac customers demand answers as bank hit with third online and mobile banking outage this week

There are fears Westpac has fallen victim to a cyber attack after customers were met with online blackouts for a third straight day.

Wednesday’s disruption impacted millions of customers, with one telling 7NEWS they could not access their cash and could not even pay for petrol because their cards were not working.

WATCH THE VIDEO ABOVE: Fears Westpac has fallen victim to cyber attack.

Westpac has not revealed what is behind the ongoing disruptions, which also blocked customers from its mobile app and online services for hours on Monday and Tuesday.

Monash University cyber security professor Nigel Phair described the outages as “extremely rare” and “extremely unusual” for modern banking systems.

7NEWS understands the ongoing issues have been referred to the government’s lead cyber security agency, with the major concern that the big four bank has been compromised.

“When something like that happens it enlivens the cyber security part of our government,” Treasurer Jim Chalmers said.

Experts say Wednesday’s disruption has the hallmarks of a “denial of service” (DoS) attack, preventing users from accessing services they would usually be able to.

Westpac has refused to rule out a cyber attack or hack but did say there has been no risk to customer data or accounts, which fits the “denial of service” theory.

“Money and data are safe enough, it’s the inconvenience that goes with it all,” Phair said.

Customers also pondered whether the bank has a security issue.

“Is it a bad systems update? Sorry — the public needs more now,” one customer said on social media.

“We need a proper statement of what the issue is and how you will resolve it.”

Westpac thanked customers for “your patience” and said again it was “sorry for the disruption”.

“In recent days Westpac customers may have experienced issues logging into their mobile or online banking,” the bank said in a statement shared on X, formerly Twitter.

“We’re sorry for the disruption. We know how important it is to have access to online banking.

“Our teams have been working around the clock and services are restored. We’ll continue to actively monitor the situation. You do not need to take any action.

“Customers are encouraged to be vigilant of potential scams at this time as some scammers may use a service disruption as an opportunity to impersonate the bank, offering help.”