This article explains how to hide the user list on the login screen. This adds another layer of security by requiring the person logging in to not only know the password but also the username. Remember, in Ubuntu the username is case sensitive just like the password; If you type it wrong , you will not get past the login screen.

Click on Applications > Accessories > Terminal and type (or copy & paste) the following line:

The next time you login you will see the change.