Account Security Issue FAQs
We have confirmed, based on a recent investigation, that a copy of certain user account information was stolen from our network in late 2014 by what we believe is a state-sponsored actor. The account information may have included names, email addresses, telephone numbers, dates of birth, hashed passwords (the vast majority with bcrypt) and, in some cases, encrypted or unencrypted security questions and answers. The ongoing investigation suggests that stolen information did not include unprotected passwords, payment card data, or bank account information; payment card data and bank account information are not stored in the system that the investigation has found to be affected.
来源：
https://help.yahoo.com/kb/account/SLN27925.html?impressions=true