The fallout continues from the huge Yahoo data breach affecting 500 million accounts - various other companies provide email using Yahoo's services.
For example BT and Sky. So if your email account is from BT or Sky, your security may well have been compromised.
It is time to leave Yahoo mail behind. I strongly recommend moving to Gmail.
If you have a Yahoo account, as a minimum:
Change your Yahoo password.
Make sure that you haven't used the same password anywhere else.
Yahoo has admitted that security questions and answers have also been grabbed by the hackers, you should be careful to ensure that they don't also come back to haunt you.
It's easy to imagine how a hacker could - perhaps with a little dab of social engineering - try to use the answers to secret questions to trick other online services into providing them access to accounts.