Commonwealth Bank of Australia (CBA) has experienced problems with its NetBank online banking system and other payment channels that have affected as many as 200,000 customers.
Many transactions initiated by NetBank customers between Friday and Monday were duplicated. Other customers found account balances of tens of thousands of dollars had disappeared, while others report transfers not being completed or being credited with funds that aren't theirs.
CBA now says it has identified the cause of the problem, and in a news item posted to the NetBank website on Tuesday afternoon it said it would resolve the situation overnight. But it has declined to go into further detail.
"We have a current issue affecting the balance on a number of customers' accounts where transactions were performed on the 22nd, 23rd, 24th of November," it said.
"We have identified a fix to this problem which will be resolved overnight."
Although it is thought that the problem mainly affected transactions initiated online, there have also been reports of ATM, phone banking and EFTPOS transactions being affected.
A statement from the bank apologised to customers affected by the processing error and said those in immediate need of cash should visit one of its branches.
It also insisted no fees or interest would be charged to customers as a result of the problem.
Earlier this year CBA began a four-year project to upgrade its core banking system. It has retained the services of Accenture to help it migrate to the SAP for Banking platform as part of a A$580 million legacy system replacement programme. But it said it was going to retain its existing CRM and Internet banking systems to help mitigate the project's risk.