The computer system executes environment classification of classifying a plurality of subsystems, each being a physical or virtual computer system, into one or more environment groups being one or more groups. The computer system stores classification result data which is data representing a relationship between the environment group and the subsystems belonging to the environment group. The computer system selects, from the classification result data, the environment group to which the subsystem having undergone a problem belongs. The computer system generates a reproduction subsystem which is a virtual subsystem virtually reproducing the subsystem for each of the subsystems belonging to the selected classification result group. The computer system applies the countermeasure to at least one reproduction subsystem for the purpose of verifying the countermeasure for the problem.