Voice calls for free: How the black market establishes free phone calls — Trapped and uncovered by a VoIP honeynet

The number of Voice over IP systems and the number of Session Initiation Protocol users is constantly increasing. The new Voice over IP infrastructures are connected with the traditional Public Switched Telephone Network and attacks against the phone infrastructure are becoming more imaginative. The attacks can cause financial losses, e.g., attackers steal money or incur costs for the victim. We analyze the current status of toll fraud attacks by analyzing real-world attacks collected in a Voice over IP honeynet solution. Based on the detailed data about real attacks, the creation or adaption of existing prevention mechanisms is possible in order to avoid toll fraud attacks in live environments.