[Logician]

This cant be possible considering the fact that search engine spider is not a member either.

One way to make it possible is to use a trick though: You can create a PHP script which gets threads from your board and give the address of this script to spider and hide it from other users.

2 Important question at that point:

1- What's the point of opening your threads to SE spiders when they cant address vb threads (if you dont use a special hack). SE dont register vb pages since they are dynamic.

2- What's the point of registering your "private" threads to search engines when you dont want them accessed by non members? If you register them, everybody will be able to visit them via search engine link..