Administrator setting to warn users when chatting out of the domain.
Admins can now enable a setting that will show users a warning that they are chatting with someone outside of their own domain. When warnings are enabled for users chatting outside of their domain, group chat conversations will be split when the first person from outside the domain is added to the discussion. This will prevent external users from seeing previous internal discussions.
Note that these features are only available in the desktop UI. Google is working on adding them to the Hangouts mobile apps soon.
For more information, click here:
Editions included: Google Apps for Business and Education