/kickban user Bans members for joining or being added to your group chat Skype room.
This command by admin in a Skype Group chat adds users to a Ban list. Even if you make a room not joinable, others can still add people. This never made sense. In Moderated rooms (which should be the default - its not in Classic on Cloud rooms), Admin can make it possible with the /set banlist or the /kickban commands to ban users from either joining or being added by others (even if joining is not enabled).
You really should add Group as a category for these Skype Ideas!