After a long time without writing because of different reasons I´m going to begin a group of articles trying to cover different type of attacks against any of the components of a common VoIP (Voice Over Internet Protocol) infrastructure and how to stop them. If you are beginning in this world of VoIP I recommend you to read Building Telephony Systems with OpenSIPS 1. 6 where the authors go through basic theoretical and practical skills needed to implement a complete system. T his time, I will start with VoIP Eavesdropping attack, as the name suggest it consists on listen a conversation without speakers consent. This attack existed in the traditional telephony systems and nowadays is also possible against VoIP ones (and other protocols too, in example bluetooth). As you can imagine we are in front of a classic sniffing attack so, first of all, we need to gain access. Any of the techniques you know are ok, moreover, there are another specific ways for this kind of systems of ...