First of all you should know what is Task Manager, Task Manager provides information about applications currently running on your system, the processes and memory usage or other data about those processes, and statistics about memory and processor, performance and your internet usage.
So going to main topic, here are steps to block Task Manager:-
1. Go to Start menu .
3. Then type “Gpedit.msc” without commas or like me you can only type group policy.’
4. It will open Local Group Policy Editor window.
5. Now navigate to User Configuration -> Administrative Templates -> System -> Ctrl+Alt+Del Options and open Remove Task Manager.
The Default state is not Configured It means your Task Manager is enabled, To disable task maager select enable. To enable task manager select disable
6. Now click on ok .
You can now check your task manager by ctrl+alt+del, It will show you message like that.