Fast user switching allows a person to quickly log into the computer with a different account. While only a minimal security risk, when a second user is logged in, that user might be able to see what processes the first user is using, or possibly gain other information about the first user. In a large directory environment where it is difficult to limit login access, many valid users can login to other user's assigned computers. Rationale: Fast user switching allows multiple users to run applications simultaneously at console. There can be information disclosed about processes running under a different user. Without a specific configuration to save data and log out, users can have unsaved data running in a background session that is not obvious. Impact: When support staff visits a user's computer console, they will not be able to log into their own session if there is an active and locked session.
Solution
Perform the following to disable fast user switching: Graphical Method: Open System Preferences Select Users & Groups Select Login Options Uncheck 'Show fast user switching menu as...' Terminal Method: Run the following command to turn fast user switching off: $ sudo /usr/bin/defaults write /Library/Preferences/.GlobalPreferences MultipleSessionEnabled -bool false Profile Method: Create or edit a configuration profile with the PayloadType of .GlobalPreferences Add the key MultipleSessionEnabled Set the key to </false>