Kiwibank says it's working to shut down a fraudulent website posing as the bank's, which tries to lure people to enter their online banking details.
The bogus site sends a generic message to people by email, advising that their attempt to enter the Kiwibank site has failed.
It then offers two options which both link to the false Kiwibank site.
Kiwibank spokesperson Bruce Thompson says no bank would contact its customers asking them to enter their internet banking details online.
He says all banks experience internet banking scams at some point and he advises Kiwibank customers to never disclose their personal bank details.
Mr Thompson says Kiwibank's internet service providers are working to close down the site which has been in operation for about two days.
He says internet scams happen often - once one site is quashed a new site opens.