Actually, I do

I have a situtation where hazard report information is placed in a forum. The thread
may affect all the groups or a combination of those groups. If a hazard does not affect a group it is important to keep the existence of the title and information from them.
If I prevent groups from just seeing the forum as you stated it would require me to have multiple forums which could get out of hand. ie.. 300 reports would equal 300 forums.
If I was able to hide the thread using your hack then I would only have 1 forum for all groups to go to and the groups would only be able to view titles and threads they are given access too.
BTW thanks for the fast reply