Yahoo has been awarded the gold medal for the largest breach in history at 1 BILLION. Oh, they also hold the silver medal too from a couple months ago with a half Billion of users compromised. This is a good time to change your Yahoo password and enable 2 step authentication on all of your accounts.
The breached users haven’t been added yet, but when they do you can see if your email was one of the victims at https://haveibeenpwned.com/
If you reused your Yahoo password to another account, you will want to change that account’s password as well. To read more about the breach visit https://krebsonsecurity.com/2016/12/my-yahoo-account-was-hacked-now-what/