We are aware of the issue and understand Yahoo is conducting an active investigation of this matter. We have limited information and understanding of the impact, at this time. As always, we recommend that customers regularly change passwords for services such as email and Fios.
For account customers that are receiving Account Locked Temporarily, please be advised this cannot be cleared and there will be a wait of 12 hours to attempt a password change. This account lock would be triggered from multiple bad login attempts and/or multiple password changes.
Here is a link to Yahoo Customer Care: https://help.yahoo.com/kb/SLN26180.html