What to Do If You Suspect Your YAHOO account has been Hacked?

Don’t panic!  Follow these steps if you have a YAHOO account.

1. Change your password to a high strength secure password with letters numbers and characters.
2. 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