Leaked information hasn't yet led to theft.
Officials say some information about 86,000 Long Island credit union members was visible on the Internet for a month.
Bethpage Federal Credit Union on Long Island notified those affected on Tuesday.
The head of the credit union, Kirk Kordeleski, says no accounts have been compromised and no money has been lost.
Newsday says the employee who made the computer error has resigned.
The leaked information included names, addresses, dates of birth, Visa debit card numbers and expiration dates. It also included members' savings and checking account numbers.