How can I hide the drop-down list of domains that appears on the logon screen of Windows XP and later machines?

A. To remove the domain drop-down list from the logon screen and force users to use their full user principal name (UPN), perform these steps:

The logon screen will no longer show a drop-down list for domains, and users will need to enter the full UPN to log on. For example, the user of an account called John in domain savilltech.com will enter the logon name [email protected].