Check out this new ArcGIS Blog:
ArcGIS has a powerful sharing model that enables its members to easily share content items such as maps, apps, scenes and files with their desired audience. Whether the audience is the entire 7.6 billion people in the world, or a few members of your company, ArcGIS Online has the infrastructure and security to get your mapping content to the right people quickly. The sharing settings of an item control both the findability and security of items in ArcGIS Online. This article will describe some common sharing scenarios and the security and findability impacts of each scenario.