Users can see and send messages to users from other groups?

Is there a way to limit the list of visible users to only users from the same group?
Basically, our client can see the list of ALL users created in the system, regardless of their affiliation with the client’s group. I want to limit that or disable online chat altogether.

Yes I’m working on implementing this now as part of the agent redesign. Agents will see all users. Customers will see users based in groups.