Without this, users with no permissions CAN view threads if they know exact url. Also "next thread" and "previous thread" can be used to see other threads. Also if you search for some user's posts you'll be able to open listed threads. I fixed this problem on 3.0.x by editing showthread.php as shown above.
Quote:
Originally Posted by KirbyDE
This can be easily done as a Plugin - no need for File Edits.