Security for portal areas helps control who has access to an area and what rights they have based on their membership in a site group. You can customize security for each area in the portal by adding, editing, or removing users, cross-site groups, or site groups.
Security settings on a parent area will be applied automatically to all of its subareas. However, if you customize the security on a subarea, the subarea will no longer inherit changes made to the parent area.