With this Tweak you can disable show last user name.

To change this, follow the next steps:

1. Open the Registry Editor click on the Start button on your taskbar, then click on Run and type "regedit" and click on OK to start the regedit utility.
    
2. Expand HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System (see picture 1).
   
   

   Picture 1

3. Create a new DWORD value, or modify the existing value, called "dontdisplaylastusername" and edit the value according to the settings above.
    
4. The modifications you made will be in effect after you logout or reboot your PC.