A community owner or a system administrator can control the various aspects of the access control during or after creation of the community. Note that each setting described in the Available Settings section is independent of each other. In other words, selecting one option for a setting will not influence the behavior or selection of the other settings. For instance, a community with (unrestricted) membership can be unlisted or its content can be made secured. Owner of a community can customize the access control based on the nature of the community. The two most common configurations are explained here.
A public community is open for anyone to join and gain membership. The community is listed in the community categories and can be browsed and searched by anyone. The content posted on community is also searchable and accessible to anyone.
Communities created on previous release of Portal Server software are considered public communities and will operate like a public community when the system is upgraded to this release of the Portal Server software.
A private community is the most secure form of a community. It is hidden from the community categories thus cannot be browsed nor searched. Private community is a community that is unlisted, secure, and having restricted membership. The community owner can invite or manually add users to the community. The content of the community is protected from non-members such that they will not be able to view or search any posted content.