The username filter functionality allows you to restrict words or phrases from being incorporated in usernames when user accounts are created. For example, you can restrict not only offensive words and terms but also common usernames such as "admin" and "administrator," which you may want to reserve for internal use.
To restrict user names:
Navigate to Control Panel Dashboard > System Administration > Site Administration > Content/Site Security > Username Filters.
Click inside the text field and enter the word you want to restrict.
Click Save Changes.