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Description:  

Specifies the screen saver for the user's desktop.

If you enable this setting, the system displays the specified screen saver on the user's desktop. Also, this
setting disables the drop-down list of screen savers in the Screen Saver dialog in the Personalization or
Display Control Panel, which prevents users from changing the screen saver.

If you disable this setting or do not configure it, users can select any screen saver.

If you enable this setting, type the name of the file that contains the screen saver, including the .scr file
name extension. If the screen saver file is not in the %Systemroot%\System32 directory, type the fully
qualified path to the file.

If the specified screen saver is not installed on a computer to which this setting applies, the setting is ignored.

Note: This setting can be superseded by the "Enable Screen Saver" setting.  If the "Enable Screen Saver"
setting is disabled, this setting is ignored, and screen savers do not run.

Supported on: At least Windows 2000 Service Pack 1.
Force specific screen saver
Description Gpedit Regedit CMD Back VBScript PowerShell Script
Gpedit:   

Please perform the following steps:

Please go to Pearl button (Start) and click on the Search programs and files
For more information about the change from Start to Pearl button click here
Type gpedit.msc and press Enter
In the Group Policy window please navigate to User Configuration -> Administrative Templates ->
Control Panel -> Personalization and open Force specific screen saver.
Not Configured -> is the Default state
Enabled -> apply this GPO
Disabled -> this GPO will not be applied

To finish press ok button and close Group Policy window.
Type regedit and press ok
Please confirm User Account Control pop-up
Microsoft official disclaimer

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by
using another method. These problems might require that you reinstall the operating system. Microsoft
cannot guarantee that these problems can be solved. Modify the registry at your own risk.

Note: This registry key is created by Group Policy when this GPO is Enable. The GPO Default state is Not
Configured -> this registry entry is not present. For Disable this registry entry is not present.

Please navigate to HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Control Panel
\Desktop
and locate SCRNSAVE.EXE registry key
Regedit:          

Please perform the following steps:

Please go to Pearl button (Start) and click on the Search programs and files
For more information about the change from Start to Pearl button click here
   
   
Double click on SCRNSAVE.EXE and edit the value:

To Enable:
Change the data value with:
SCRNSAVE.EXE = %Systemroot%\System32\Mystify.scr

To finish press ok button and close Registry Editor window

Note: Manual editing of this registry key will not be reflected in Group Policy. If you modify this GPO from
Group Policy this registry key will be rewritten.
Type cmd, right click on cmd icon under the Programs and click on Run as administrator
Please confirm User Account Control pop-up
Please select, right and copy a registry key from below, then right click on command prompt window
, select Paste and press Enter

Enabled:
REG add "HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop" /v SCRNSAVE.EXE /t REG_SZ /d %Systemroot%\System32\Mystify.scr /f

Not Configured:
REG DELETE "HKCU\Software\Policies\Microsoft\Windows\Control Panel\Desktop" /v SCRNSAVE.EXE /f

Note: Manual editing of this registry key will not be reflected in Group Policy. If you modify this GPO from
Group Policy this registry key will be rewritten.
CMD:          

Please perform the following steps:

Please go to Pearl button (Start) and click on the Search programs and files
For more information about the change from Start to Pearl button click here
   
VBScript:          

Const HKEY_CURRENT_USER = &H80000001
strComputer = "."
Set oReg=GetObject("winmgmts:{impersonationLevel=impersonate}!\\" & _
strComputer & "\root\default:StdRegProv")

strKeyPath = "Software\Policies\Microsoft\Windows\Control Panel\Desktop"
oReg.CreateKey HKEY_CURRENT_USER,strKeyPath
strValueName = "SCRNSAVE.EXE"
'Enabled
strValue = "%Systemroot%\System32\Mystify.scr"
oReg.SetStringValue HKEY_CURRENT_USER,strKeyPath,strValueName,strValue
'Not Configured
'oReg.DeleteValue HKEY_CURRENT_USER,strKeyPath,strValueName
PowerShell Script :          

Enabled

$RegKey = "HKCU:\Software\Policies\Microsoft\Windows"
If(Test-Path ($RegKey + "\Control Panel"))
{
 $RegKey = "HKCU:\Software\Policies\Microsoft\Windows\Control Panel"
 If(Test-Path ($RegKey + "\Desktop"))
 {
   $RegKey = "HKCU:\Software\Policies\Microsoft\Windows\Control Panel\Desktop"
    ##Enabled
    New-ItemProperty -path $RegKey -name SCRNSAVE.EXE -value %Systemroot%\System32\Mystify.scr -PropertyType String -Force
 }
 else
 {
   New-Item -path $RegKey -name Desktop
   $RegKey = "HKCU:\Software\Policies\Microsoft\Windows\Control Panel\Desktop"
    ##Enabled
    New-ItemProperty -path $RegKey -name SCRNSAVE.EXE -value %Systemroot%\System32\Mystify.scr -PropertyType String
 }
}
else
{
 New-Item -path $RegKey -name "Control Panel"
 $RegKey = "HKCU:\Software\Policies\Microsoft\Windows\Control Panel"
 New-Item -path $RegKey -name Desktop
 $RegKey = "HKCU:\Software\Policies\Microsoft\Windows\Control Panel\Desktop"
  ##Enabled
  New-ItemProperty -path $RegKey -name SCRNSAVE.EXE -value %Systemroot%\System32\Mystify.scr -PropertyType String
}

Not Configured\Disabled

$RegKey = "HKCU:\Software\Policies\Microsoft\Windows"
Remove-ItemProperty -Path($RegKey + "\Control Panel\Desktop") -name SCRNSAVE.EXE
If( (Get-Item -Path($RegKey + "\Control Panel\Desktop")).ValueCount -eq 0 -and (Get-Item -Path($RegKey + "\Control Panel\Desktop")).SubKeyCount -eq 0)
{
 Remove-Item -Path($RegKey + "\Control Panel\Desktop")
 If( (Get-Item -Path($RegKey + "\Control Panel")).ValueCount -eq 0 -and (Get-Item -Path($RegKey + "\Control Panel")).SubKeyCount -eq 0)
 {
   Remove-Item -Path($RegKey + "\Control Panel")
 }   
}
Up Back
   
   
   
Result
By Default you have access to "Screen saver" under Start -> Control Panel -> Personalization -> Screen
Saver.
You can set a specific Screen Saver and prevent users from using "Screen saver" using Group Policy or
modify the specific
registry key.  

Note: If you want to set a specific Screen Saver and prevent a specific user from using "Screen saver" you
need to modify or add the
registry key under his SID.