Bulk add users to new usergroup

[pjkcards]

I want to create a new usergroup A which everyone on the forum is part of. I want it to be similar to Registered Users, except there will be 1 forum where if you get removed from usergroup A, you can no longer post.

I've created the usergroup, then modified the forum permission for that group. But how do I add all users on the forum to the group?

The idea is that everyone is part of it, but when we want someone no longer able to post, we can simple remove them from that additional usergroup.

Thanks.