[Freeswitch-users] Calls without registration

Hello, due to an open firewall some robots could get into my network and start some calls (11.000!) over my PSTN gateway. I looked through the data and those robots didn't registered themselve, they just placed the call on the internal profile and succesfully got through the dialplan. How is it possible that they can make calls on the internal profile (Port 5060) without registration and is there a variable for sofia to don't allow those calls. Is there anything else I can do appart from checking the source IP Address in the dialplan? Thanks, Paul