Around 4200 Kiwibank customers have been sent a bank statement that's not theirs in a significant privacy breach.
The customers saw someone else's transaction history under their correct account number, name and address, Kiwibank confirmed to 1 NEWS.
Some were sent via email while others were accessed through online banking.
"We have written to 4200 customers who received the wrong transaction history via email asking them to delete it immediately and we have deleted all incorrect statements sent via internet banking," a Kiwibank spokesperson told 1 NEWS today.
"We are also writing to customers whose transaction history may have been shared with the wrong person, apologising for the error and outlining the steps we’ve taken to protect their transaction history."
The bank says it believes the impact on those customers is "low", but it'll work with them to address any concerns they may have.
Kiwibank has contacted the Privacy Commission to "explain what has happened and how we have moved quickly to address this issue".