lock computer via screen saver

This will lock screen after 1 minute and prevent users to change screen saver settings
scrnsave.scr stands for "Blank" screensaver.

Create this as an user script:

reg add "HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop" /v ScreenSaveActive /d 1 /f
reg add "HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop" /v ScreenSaveTimeOut /d 180 /f
reg add "HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop" /v ScreenSaverIsSecure /d 1 /f
reg add "HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop" /v "SCRNSAVE.EXE" /d "C:\Windows\system32\scrnsave.scr" /f

Next one is much user friendly cause it lets user to choose the screen save which likes better:

Remove customization:

reg delete "HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop" /v ScreenSaveActive /f
reg delete "HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop" /v ScreenSaveTimeOut /f
reg delete "HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop" /v ScreenSaverIsSecure /f
reg delete "HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop" /v "SCRNSAVE.EXE" /f

These settings also can be found under Group policy. Just remember apply this policy to user objects NOT computer: