Yahoo has confirmed that the names, email addresses, date-of-birth, telephone numbers, hashed passwords, and unencrypted security questions and answers of 500 Million accounts were hacked in 2014.  https://investor.yahoo.net/releasedetail.cfm?ReleaseID=990570

It is recommended you change your security credentials on any service that shares the same information.  Yahoo itself is committed to pushing their new "Account Key" app or give them your cell phone number (for hackers to steal that too) for 2-factor authentication.