The police have confirmed the full details of 34 individuals were compromised in the gun buy back scheme, with about another 500 having their names and addresses accessed.
Personal information about the gun owners, such as name, address, contact number, firearms licence number and bank account details, were made available to dozens of firearms dealers through its gun buyback website.
The police say a systems audit has confirmed there was only one login from a dealer with legitimate access.
They've been in touch directly with that person, who's assured them the information "has not been used in any way, shape or form".
But the Council of Licenced Firearm Owners insists at least 19 people accessed sensitive information.
RNZ political editor Jane Patterson has the story