Hackers have taken names, addresses, contact details and expired credit card numbers from the AA Traveller website used between 2003 and 2018.
AA travel and tourism general manager Greg Leighton said the data was taken in August last year and AA Traveller found out in March.
He said a lot of the data was not needed anymore, so it should have been deleted before the breach.
"You should be able to give your data and for that to be secure. We understand that and respect that and are incredibly sorry."