Electronic attacks such as spoofing are becoming an increasing threat for satellite-based navigation receivers. The aim of this paper is to develop a preventive method against such electronic attacks. In our scheme, the localization system uses four different Global Navigation Satellite Systems (GNSSs): GPS, Galileo, GLONASS, and Compass. The signals received from these satellite systems will be fused inferentially and will be tracked according to a linear model. The linear model that we developed is solved with a Kalman filter and simulated under different scenarios. When a discrepancy is detected in the output of one of the GNSS receivers due to spoofing, it is excluded from the fusion.