An expat New Zealander is concerned about the security of his financial information after his wife was sent the full details of another person's KiwiSaver account.
He says he is concerned about the security of his own information after the breach.
New Zealander Tim Hoffman and his wife live in San Francisco. They had been seeking their KiwiSaver details from the Kiwi Wealth scheme run by Gareth Morgan Investments (GMI).
GMI is a sister company of Kiwibank, and both are part of New Zealand Post's Kiwi Group Holdings.
Mr Hoffman said he and his wife needed to give their retirement savings details to the United States tax department.
After a number of weeks of trying to get them, he said his wife was last week emailed the full details of another woman's account, including balances over the past few years, address, phone number and IRD number.
He said that made him worry about the security of his own details.
"My main concern is that you have a financial institution that's trusted by many New Zealanders that cannot be trusted with our financial information.
"Having used both Kiwibank and Kiwi Wealth over the last eight years, we are now unable to trust that our transaction history will be kept in a secure manner."
Mr Hoffman said despite calling and emailing Kiwi Wealth about the breach he had not heard back from them.
GMI chief executive Ian Burn said the company took such matters very seriously and he was disappointed it had happened.
He said GMI would be able to respond more fully once it had more information.