If you accidentally give someone permission to connect to one of your sources, or you decide that you no longer want them to have permission, you can revoke all permissions (for all users) by clicking the ‘Clear Permissions’ button in the Privacy preferences.
Any new connections to any of your sources will require your permission, and any existing connections will require permission to be re-granted (you will be presented with an access control pop-up for each connection, which can be allowed or denied individually).