Yahoo reveals a data breach may have affected more than a billion accounts.
It says back in August 2013, hackers may have stolen information including names, e-mail addresses, phone numbers, birthdates and security questions and answers.
But the company believes bank account and payment card information were not affected.
Yahoo believes the breach is different from the one it disclosed in September.
It says it is working closely with law enforcement to investigate the hack.
Yahoo says it has also taken steps to secure user accounts like notifying potentially affected users and requiring them to change their passwords.