Consider the following scenario:
You have a Windows 10 version 1703 PC (or an earlier version of Windows 10), preinstalled by the Original Equipment Manufacturer (OEM).
You then upgrade the system to Windows 10 version 1709.
You then Reset the PC, selecting the option to Keep my files.
When the reset is completed, the Windows sign-in screen may display the Administrator account and prompt the user for the password. When you click within the password box for the Administrator account, the user accounts that were added to the PC prior to the reset then appear as options for signing into Windows.
If you then select one of your user accounts and sign into Windows 10, whenever you restart Windows, the sign-in screen again displays the Administrator account.
Due to changes in Windows 10 version 1709, while restoring the registry keys to the OEM’s original factory settings, the reset process may include the registry key for the automatic logon to the default Administrator account used during the pre-installation process. This can occur if the OEM utilized the “auditSystem” and “auditUser” attributes in the unattend.xml file.
Important - This section contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
To prevent the Administrator account from appearing on the sign-in screen whenever you restart Windows, modify the registry key that sets the automatic logon:
From the Windows sign-in screen, click the password box for the Administrator account. The other user accounts on the PC should then appear in the lower left corner.
Select one of your user accounts that has administrator-level permissions and sign into Windows.
In the search box on the taskbar, type regedit. Select the regedit Run command in the search results. Accept the user prompt to launch the Registry Editor.
In Registry Editor, navigate to the following registry key and click on the folder in the left pane: Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon.
In the right pane, click on AutoAdminLogon, and then in the Menu, select Edit and then Modify…
Set the Value Data to 0, and select OK.
Close Registry Editor and restart Windows.