A method of selecting, for at least one service of an information system and depending service(s), at least one countermeasure to be implemented against at least one cyber attack, the method includes: identifying elements of the service exposed to the cyber attack(s), calculating a risk mitigation level of each countermeasure with respect to the cyber attack(s), ranking the countermeasure(s) on the basis of a parameter which is at least a function of the risk mitigation level, simulating the impact of the countermeasure(s) on the service and the depending service(s), the countermeasure to be implemented being selected at least as a function of result of the simulation.