With the implementation of this Feature Request https://www.nomachine.com/FR04O03397 in version 6, it's now possible to close the NoMachine program from its menu.
This will shut down all the server side services and prevent connections to your computer. Shutdown the server means to terminate all NoMachine services. If you close the program, you will not find any active NoMachine service among your Windows services.
A user with administrative privileges is requested to complete the operations.
1) Click on the Monitor (the !M icon) in the system tray to open the menu:
2) Click on 'Close the NoMachine application'.
3) You will be asked if you want to run the NoMachine application at the next startup: choose 'No' to disable the automatic start of NoMachine services at boot time.
You may be also interested to:
Alternative ways to shutdown NoMachine and disable the automatic startup at boot time
How to disable access to your computer without stopping all services: