Login or usernames can be identical to your display name on the front-end, for example as an author of a blog post. Or available in a RSS Feed etc. This creates an instant vulnerability as you login name is available to anyone.
How to change your display name
You can change display names, but the options are limited as they are based on the first entries while creating the user. In this example you can see where under the user editing screen (WordPress – Users) you can change the display name so it does not correspond with the login name.
In the above example you are able to choose between a combination of your first and last name. Although you’re changing your display name it still connected and might be easy to guess. We therefore suggest to make sure there’s no direct link between your username and display name.