Restrict Group Visibility
You can make groups private by using the Restrict Newsgroup Visibility option when you add or edit Directories properties. Because private groups are not visible to users who do not have permission to read or post articles, there is no access to those newsgroups or the information they contain.

Note  For best performance, it is recommended that you disable the Restrict Newsgroup Visibility option on virtual directories where anonymous access is allowed. Otherwise, the server will unnecessarily check permissions for each newsgroup when processing the LIST command.

Select Restrict Group Visibility if you want only clients with read or post permission to be able to see the newsgroups under the specified directory. Because of the overhead in processing permissions on a per-group basis, this option may cause a loss in performance. Clear Restrict Group Visibility to allow full access to the newsgroups.