What is telecom fraud?

Telecom Fraud is defined as: the intent to defraud another of the lawful charge for telecommunication service.

Most commonly, hackers find holes in IPPBXs that are connected to the public internet by using SIP scanners and exploiting system weaknesses.  Typically these are default passwords being left in place, extensions being left unsecured, open SIP ports or incorrectly managed or non-existent of firewalls. For more information read this article.