Millions of passwords have been stolen from Google, Hotmail and Yahoo mail. If you have an Yahoo mail account, you should have already received email notifications about the account security issue this month, December 2016. See this security notice from Yahoo.
You’ll receive a prompt in the desktop version of Yahoo Mail explaining the security issue. We are encouraged to change Yahoo password or invalidate security questions and answers so that they cannot be used to access an account.
There are two account security settings that add an extra layer of security to our Yahoo account but also cause confusion to users who access their Yahoo mail on a mobile device. One is the two-step verification which will send a security code to your phone when you log in from new devices. The other is ‘Allow apps that use less secure sign in’ if this option is disabled, it block apps that use a less secure sign in method from accessing Yahoo account.
When I log on Yahoo account using its desktop version on my PC, I was prompted to turn off app access. I disabled this security option to improve the security of my Yahoo mail account without hesitation.
Later when I want to set up the Yahoo mail account on my Samsung phone, it then throws an error saying Yahoo mail setup could not finish authentication failed on my Samsung phone.
If you use a non-Yahoo mail app or other apps that use less secure sign-in technology, you will fail to set up the Yahoo account or these email apps will stop working. For example, the Mail app on Samsung errors out “setup could not finish, authentication failed”. If you try to add Yahoo mail to other mobile phones that do not meet Yahoo’s security requirements, you may also fail with similar and confusing error message like couldn’t set up account, username or password is incorrect, authentication failed, incorrect username or password, etc. In fact it is just the app access is blocked in Yahoo account security settings page.
Download and use Yahoo mail app is the workaround. Alternatively use a up-to-date more secure app to access Yahoo mail on a mobile phone or tablet. You can find more details about this Yahoo mail app access and security issue here.
Yahoo don’t recommend using apps with less secure sign in. However if you do need it, you can log on your yahoo account from a desktop, go to temporarily allow apps using old security sign in and turn it off as soon as possible.