Oct 2, 2013 (Wed): Yahoo! has introduced App Passwords, an additional way as second sign-in verification to protect its users and their data. Users are required to enter an App Password (a temporary password) into Yahoo!’s native iOS and Android apps for added protection.
Once the temporary password entered into the mobile app, the device will be logged-in, so the users won’t have to go through this step again unless they change or add another device.