restricted access

I want to set up a group for people that can only see 1 or 2 forums or sub-forums.

I set up a hidden group. Went to permissions and ticked 2 boxes (forums/sub-forums) of the forums I want them to have access to.

Then to try it out I rang up one of my friends, moved them into the group and asked them to log in again. And it didn't work. He could still see all the forums.

What have I done wrong?

Go to:
Admin panel>General>Categories and forums>click on the edit button next to the forum>Permissions>set up Permissions...

Thanks!