My 7100 is being hacked for international phone calls. I've been through the system and I can't see anything wrong. I'm having my service provider disable 011 dialing and having users change their voicemail passwords. The system is only configured for analog trunks. What else could I be looking for?
Andrew, does the 7100 have a public IP address on it? If so, blocking SIP from any address other than your provider is best practice. You may find some of the suggestions in the SIP security guide for the 7100 useful: