The National Australia Bank (NAB) sent the details of approximately 60,000 customers to an email address on a global domain rather than its .au address.
It is understood customer information was sent in error to an nab.com address rather than an email address on the nab.com.au domain.
The email contained each customer's name, address, email address, branch and account number, as well as an NAB identification number for some customers.
The bank revealed the error in December, and at the time, apologised to customers and took "full responsibility" for the error, explaining that those impacted were customers who had their accounts created by the bank's migrant banking team while they were overseas. The bank also 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, with 19,000 accounts containing less than AU$2.
In a statement made this week, NAB executive general manager for international branches Peter Coad said the bank was able to take action to ensure the group of migrant banking customers' accounts remained secure.
"Although this has been a complex process involving multiple international jurisdictions, all parties -- including the email account owner -- are taking this extremely seriously and NAB is working hard to resolve this matter for our migrant banking customers as soon as possible," the statement reads.
"From our productive and helpful discussions with the email account owner, we understand that the email address to which the correspondence was incorrectly sent is not actively used and our customers' emails have not been wrongfully used. We are confident that there has been no unusual activity associated with these migrant banking accounts and we continue to monitor 24/7."
Reports indicate the domain name nab.com belongs to David Weissenberg who owns domain names through his company Real Assets Limited, which includes a handful of adult content websites.
At the end of last year, NAB experienced three system outages in the space of seven days.
The first hit its internet banking, customer call centres, and payments processing as a result of a "number of system outages" experienced the night before.
The bank's customers Australia-wide were then prevented from using their bank cards in ATMs or at EFTPOS terminals, with the outage also affecting NAB merchant terminals and its health claims and payments system (HICAPS), a payment solution for health care providers.
The third outage meant customers were unable to access their internet banking.
The bank also reported a 94.4 percent statutory profit slump to AU$352 million for the 2016 financial year, citing technology investments as a main contributing factor.