National Bank of Canada says a website error may have exposed the personal information of nearly 400 of its customers, including their names, birthdates, phone number and email address.
The Canadian lender says in a statement the problem related to an electronic form on its website and did not expose clients' banking information, social insurance numbers or addresses.
The bank says a customer filling out an online form to make a branch appointment may have been able to see the data entered by a previous user.
National Bank says it was notified earlier this week about the problem, which lasted a few days.
The lender adds the incident was the result of human error while setting up the online form, and was resolved immediately.
The bank is contacting the nearly 400 potentially-affected customers to offer free credit monitoring.