Westpac has apologised for a technical glitch that happened just before Christmas causing some customers to be left hundreds of dollars in overdraft.
Hordes of customers have been put into debt after the bank did not process transactions properly.
In a social media post, Westpac said some MasterCard credit and debit card payments on the 23rd and 24th of December were not processed correctly.
Affected transactions were processed on Saturday night, the bank has said customers would not be charged for any overdrafts the issue caused.
Gorilla Technology CEO, Paul Spain, told Today FM it is a pity that it took two weeks for the bank to raise the alarm.
"It's not unique, but it is still something," he said.
"We really expected our banking systems to be robust and something we can rely on and trust."
Spain said the most likely reason for the delay was an automatic process not following through.
"Some sort of functional operation that was supposed to happen automatically within Westpac's systems or the credit card provider's systems that have failed on this occasion."
Westpac confirmed on Sunday afternoon it will work to ascertain the financial impact on individuals.
Customers affected by the glitch are advised they can visit one of its branches or call its contact centre.
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