An image forming apparatus comprising: a communicator to perform communication with one or more external devices (400, 400-2); a controller to: obtain security setting information of the one or more external devices (400, 400-2), perform a comparison between the obtained security setting information of the one or more external devices (400, 400-2) with security setting information set to the image forming apparatus to determine, based on a result of the comparison, whether it is possible to transmit or receive encrypted data between the image forming apparatus and the one or more external devices (400, 400-2), respectively, and determine a defect information corresponding to the one or more external devices (400, 400-2), respectively, in the security setting information set to the image forming apparatus based on the result of the comparison; wherein the defect information indicates an activation or deactivation change to be applied to an information item, from among information items, of the security setting information set to the image forming apparatus, corresponding to the one or more external devices (400, 400-2), set to the image forming apparatus, corresponding to the one or more external devices (400, 400-2), respectively, based on the result of the comparison; and a user interface device to output the defect information indicating the activation or deactivation change to be applied in the security setting information set to the image forming apparatus. a communicator to perform communication with one or more external devices (400, 400-2); a controller to: obtain security setting information of the one or more external devices (400, 400-2), perform a comparison between the obtained security setting information of the one or more external devices (400, 400-2) with security setting information set to the image forming apparatus to determine, based on a result of the comparison, whether it is possible to transmit or receive encrypted data between the image forming apparatus and the one or more external devices (400, 400-2), respectively, and determine a defect information corresponding to the one or more external devices (400, 400-2), respectively, in the security setting information set to the image forming apparatus based on the result of the comparison; wherein the defect information indicates an activation or deactivation change to be applied to an information item, from among information items, of the security setting information set to the image forming apparatus, corresponding to the one or more external devices (400, 400-2), set to the image forming apparatus, corresponding to the one or more external devices (400, 400-2), respectively, based on the result of the comparison; and a user interface device to output the defect information indicating the activation or deactivation change to be applied in the security setting information set to the image forming apparatus. obtain security setting information of the one or more external devices (400, 400-2), perform a comparison between the obtained security setting information of the one or more external devices (400, 400-2) with security setting information set to the image forming apparatus to determine, based on a result of the comparison, whether it is possible to transmit or receive encrypted data between the image forming apparatus and the one or more external devices (400, 400-2), respectively, and determine a defect information corresponding to the one or more external devices (400, 400-2), respectively, in the security setting information set to the image forming apparatus based on the result of the comparison; wherein the defect information indicates an activation or deactivation change to be applied to an information item, from among information items, of the security setting information set to the image forming apparatus, corresponding to the one or more external devices (400, 400-2), set to the image forming apparatus, corresponding to the one or more external devices (400, 400-2), respectively, based on the result of the comparison; and a user interface device to output the defect information indicating the activation or deactivation change to be applied in the security setting information set to the image forming apparatus.