In order to remove the logging off option from the Window, you'll have to remove the "Log Off" from the start menu and from the Task Manager as well.
1. Remove Log Off option from Task Manager
In order to remove the "log off
- Open Group Policy Editor (Start->Run->"gpedit.msc")
- On the left go to, User Configuration->Administrative Templates->System->Ctrl+Alt+Del Options.
- On the right, Enable this setting "Remove Logoff". (see figure below)

This setting does not let the user log off the system by using any method, including programs run from the command line, such as scripts. It also disables or removes all menu items and buttons that log the user off the system except from the Start Menu.

2. Remove Log Off from the Start Menu
To remove the log off button from the Start Menu, do as follows:
- Open Group Policy Editor (Start->Run->"gpedit.msc")
- On the left go to, User Configuration->Administrative Templates->Start Menu and Taskbar.
- On the right, Enable this setting "Remove Logoff on the Start Menu". (see figure below)


