SPSite.DenyPermissionsMask property

SharePoint 2013

This property will deny the rights specified by the permission mask to all users of the site collection including the site collection admin. The elevated process identity is the only exception that has full rights

Namespace:  Microsoft.SharePoint
Assembly:  Microsoft.SharePoint (in Microsoft.SharePoint.dll)

Public Property DenyPermissionsMask As SPBasePermissions
Dim instance As SPSite
Dim value As SPBasePermissions

value = instance.DenyPermissionsMask

instance.DenyPermissionsMask = value