One wish list feature contest holders frequently have is the ability to hold a private that is only visible to registered members or invite only contests that only selected members can access. Well we now have both features. Contest holders can flag a contest as a private thread that will only be visible to registered members who are logged in and will not be visible to non-registered members or to search engines. Contest holders can also choose to invite only specific members who are allowed to access a contest thread.
To the best of our knowledge, we are the first contest design site that allows contest holders the ability to hold private threads and/or invite only threads.
The only caveat to private/invite only threads at this point in time is that the thread title can appear in the "last post" column of forum indexes so we would advise not putting confidential information in thread titles. Non-authorized members/visitors won't be able to access private/invite contest threads even if they do see the thread title in the last post column.