Occasionally a system bug will pop up in the System Preferences>Network pane. An alert dialog will display indicating that network setting have been changed by another application. You try to dismiss this dialog and it continues to reappear in an endless loop. Be quick on the draw and you can dismiss the dialog by pressing the enter key and choose another pane with the mouse. Then go the the System Preferences>Security>General and check the box “Require a password to unlock each System Preference.”