Yahoo claims to have 1 billion active monthly users right now. That’s different than total users, and that number could be much higher than it was in 2013. Either way, with two separate hacks in 2013 and 2014 impacting between 1 billion and 1.5 billion accounts, it’s a good bet that yours was among them.
Even if it wasn’t, it’s not a bad idea to treat it as such. So where do you start?
Figure Out If You Have A Yahoo Account
Not all Yahoo accounts have the word Yahoo in them. Yahoo provides white-label email service to Internet service providers (including AT&T, Frontier, SBCGlobal, and Verizon in the U.S., Rogers in Canada, and BT and Sky in the U.K., among others). It’s possible, then, that your primary email account is a Yahoo account and you don’t even know it.
A quick Google search should be all it takes. If not, have a chat with your provider’s tech support.
Go Change Your Password. Like… Yesterday.
Changing your email password on your Yahoo account ISP-provided email account immediately is a very good place to start. Change your password reset questions and answers. If you have the option, you should also enable two-step verification for added security.