The paper is concerned with the material devoted to the problem of resistance of the state estiamtion (SE) procedure to cyberattacks on the system for collection and processing of PMU measurements, i.e. wide area monitoring system (WAMS), and the SE procedure itself. Based on the analysis of potential cyberattacks, which reveals the most vulnerable WAMS components, we show the conditions for a failure of the SE procedure. The method of fault tree is proposed to describe the consequences of cyberattacks on the SE procedure. The fault tree method is applied to the software of power system state estimation in WAMS environment in real time. The upper level of the fault tree represents a group of system indices, i.e. the algorithms applied in the state estimation procedure, base scheme of the EPS and measurements. The middle level represents events that cause faults, and the lowest level is the types of actions on the fault causes. Currently, the results of the analysis of the received measurement data and results of the state estimation are used to assess the level of cyber-resistance of the state estimation software.