As it stands, ArcGIS Online allows one to create “Private” groups into which confidential maps, tools and applications can be stored. The administrator of the private group can “invite” users into the group. Problem is that members (invitees) of the group can use the “Save as…” option to save a private map into their account and potentially share it to the public, which usurps the security intentions of the private group.
In ArcGIS Online, please disable the “Save as…” functionality for non-administrator members of a “Private” group.
