If you’re using Gmail then I guess that you know Gmail’s 2-step verification. This adds an extra layer of security to your online accounts.
Gmail regularly reminds you to enable 2-step verification by asking you to verify your phone number. But not many people know that Yahoo! (and Microsoft too) also offers a similar security feature.
So if Yahoo! Mail is STILL your primary e-mail then I suggest you to setup Yahoo!’s second sign-in verification for your Yahoo! accounts.
Go to Yahoo! Account Information and click on "Set up your second sign-in verification".
What I like about Yahoo!’s Second Sign-in Verification is that you can request the verification code by e-mail (non-Yahoo! e-mail address) or phone. Sometimes it’s annoying when we have to request a code every time we want to logon to Gmail (and then there’s application specific passwords and all).
With Yahoo! Mail, you can either use your security question or your phone number or both for verification. Once you’re done you’ll see the following message "Success! You’ve completed the second sign-in verification setup."
Hotmail (and Outlook.com) users can sign in with a single-use code so that you don’t have to enter your password. This feature comes handy when you’re using someone else’s computer or a shared PC.
Sign In With A Single-use Code
A single-use code lets you sign in without entering your password. This helps protect your account when you’re using someone else’s PC.