This paper presents developed model of information security threats for messaging systems with decentralized node structure. Information flows are considered, the diagram of states information in the process of interaction within the decentralized messaging system is developed. The presented security threats correspond to the FSTEC BDU classification and are also categorized by layers of the Open Systems Interoperability Reference Model. For each of the above threats, the ways of their realization were consideredand the possible source of the threat was described.