teleconsul on "Brute force on admin username"

Hi,

i have a multisite installation and more IP continuosing attempts to login to my platform using not standard administrator account.

I have also changed 2 times the username, but after a quiet period the login attempts come back with the new username.

I ask:
What is possible that username gone captured?
There is a method to avoid this problem?

I also checked guest web site integrity and the admin usernmae is used by only 3 people.
Our customers have only restricted username.

Thank a lot