This option is in the Client Settings for the GroupVPN. The last check box is "Use Default Key for Simple Client Provisioning". This feature allows Global VPN Client users to connect without entering the shared secret. This is fine as long as you have xauth enabled so users are required to enter a username and password. If xauth is not enabled, you want to disable that feature in the Client Settings so users will need to enter the shared secret.
This setting does not affect users with the VPN 8.0 (Safenet) Client.