This policy setting permits or prohibits the use of this snap-in. If you enable this policy setting the snap-in is permitted and can be added into the Microsoft Management Console or run from the command line as a standalone console. If you disable this policy setting the snap-in is prohibited and cannot be added into the Microsoft Management Console or run from the command line as a standalone console. An error message is displayed stating that policy is prohibiting the use of this snap-in. If this policy setting is not configured the setting of the "Restrict users to the explicitly permitted list of snap-ins" setting determines whether this snap-in is permitted or prohibited. -- If the policy setting "Restrict users to the explicitly permitted list of snap-ins" is enabled users cannot use any snap-in except those explicitly permitted. To explicitly permit use of this snap-in enable this policy setting. If this policy setting is not configured or disabled this snap-in is prohibited. -- If the policy setting "Restrict users to the explicitly permitted list of snap-ins" is disabled or not configured users can use any snap-in except those explicitly prohibited. To explicitly prohibit use of this snap-in disable this policy setting. If this policy setting is not configured or enabled the snap-in is permitted. When a snap-in is prohibited it does not appear in the Add/Remove Snap-in window in MMC. Also when a user opens a console file that includes a prohibited snap-in the console file opens but the prohibited snap-in does not appear.
Windows Components\Microsoft Management Console\Restricted/Permitted snap-ins
User
At least Windows Vista
HKCU\Software\Policies\Microsoft\MMC\FX:{7d3830aa-e69e-4e17-8bd1-1b87b97099da}!Restrict_Run
MMCSnapins.admx