Getting group name

I have forbidden a certain group members from seeing each other online using the Packet Filter.

It’s correctly defined, when a member goes online, the others can see their status (or send msgs, etc)…

The problem the group is listed at other places. Starting by the Offline Group, where members are listed (I removed this group), but there are other places like the Broadcast.

So, I would like to know if any of you know a “variable” (sorry, can’t remeber the correct name) to get the name of the user’s group.

For example, I have “member X” at “group Y”. I want to know if I can get “group Y” having member X’s jid.

Thanks in advance.