Don’t panic! Follow these steps if you have a YAHOO account.
- Change your password to a high strength secure password with letters numbers and characters.
- Check your alternative email address is correct.
Your YAHOO account may have been hacked if:
- Your yahoo account information/details has changed without your knowledge.
- There are logins from locations you don’t recognise on your recent activity page.
- You aren’t receiving expected emails from senders
- Your Yahoo Mail account is sending spam.
Full details here https://help.yahoo.com/kb/SLN2090.html