How to fix MySQL anonymous account security issue? How to fix this security issue on MySQL?

[!!] User '@localhost' is an anonymous account.
Do you want to remove the anon users? You can just use DROP USER to remove them. They shouldn't have any special privileges, as stated in the MySQL Docs and should not be a major problem as they're only in the localhost.

If, even removing, you still can login or something, check out this other question.