The National Australia Bank (NAB) has taken "full responsibility" and apologised for the sending of personal data of 60,000 customers to an "incorrect email address".
The email contained each customer's name, address, email address, branch and account number, as well as an NAB identification number for some customers. Those impacted were customers who had their accounts created by the bank's migrant banking team while they were overseas.
"This error does not impact customers who set up an account in Australia," the bank said in a statement on Friday afternoon. "We take the privacy and the protection of our customers' personal information extremely seriously.
"The error was caused by human error and identified following our own internal checks and as soon as we realised what had happened we took action."
NAB said it had not seen any unusual activity on the affected accounts, and 40 percent of those customers had either closed their accounts or not used them in 2016. The bank said 19,000 accounts contained less than AU$2.
"We are sorry for this error and we will continue to work hard to improve and strengthen our processes," the bank said.
NAB said it had notified the Office of the Australian Information Commissioner and the Australian Securities and Investments Commission.
In October, NAB posted a AU$352 million statutory net profit for the 2016 financial year and praised its reduction in "technology incidents".