Many mobile network operators rush to upgrade their networks to 4G/LTE from 2G and 3G, not only to improve the service, but also the security. The Diameter protocol - the successor of SS7 in Long Term Evolution (LTE) networks is believed to offer more protection to the network itself and to the end-users. However, also Diameter offers a rich functionality set, which can be also exploited and misused, if the network is not properly protected. We will show in this lecture, how data interception (MiM) can be done via the diameter based interconnection link.