By default, the Windows default Shell (Explorer.exe) is initiated to show the user desktop. You can change this behavior by replacing the Explorer.exe with your own application name at the registry.
Key: HKEY_Local_Machine\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
Entry Name: Shell
Replace Explorer.exe with your application name. Please make sure you enter the exact path of the application. You need to ask your users to log off and log on for the changes to take affect.