Q: Was my account hacked?
A: Experts I’ve spoken to believe Yahoo has about a billion active accounts. So, yes, it’s very likely your account’s password is compromised, and probably most of the other information you at one point entrusted to Yahoo. According to a statement from the company, the stolen user account information may have included names, email addresses, telephone numbers, dates of birth, hashed passwords (using MD5) and, in some cases, encrypted or unencrypted security questions and answers.”
Q: I’m not sure if I have a Yahoo account. How do I find out?
A: This is a surprisingly complex question. Thanks to the myriad mergers and business relationships that Yahoo has forged over the years, you may have a Yahoo account and not realize it. That’s because many accounts that are managed through Yahoo don’t actually end in “yahoo.com” (or yahoo. insert country code here).
Read more about the Yahoo Hack here : krebsonsecurity.com/2016/12/my-yahoo-account-was-hacked-now-what/#more-37257