If you need to see a working example of that, check out my malware removal board (link in my signature) - all the website pages (links at top of pages) are posts from inside such 'hidden' forums, including the MWR University page which will NOT show the post without being registered and logged into the forum.
See if you can find the actual topics !!!!
phpBB: The All Important Rules - Bertie Bear 3.0 - No support via PM system - use the forums please.
phpBB v2: Retirement (1/1/2009) : phpBB v3: Read Me Topic - Custom BBCodes - Support Template
Matthew 7:7"Ask and it will be given to you; seek and you will find; knock and a door will be opened to you."
My Links: MS MVP (Consumer Security) - Malware Removal:University - Own Forum: Custom BBCode testing