The asterisk means the ACL was inherited, rather than being set directly on that element. See page 123 of the 4.6 Administrators Guide.
Internal ACL is described in the IS Administrators Manual 4.6 release page 118: “Allows only users in the Administrators and Developers groups access to a service and denies all other users. The server assigns this ACL to built-in utility services shipped with the server”.
Generally, Internal is set on services that should not be called from outside the IS.
#webMethods#webMethods-General#Integration-Server-and-ESB