A security system for software to be input to a closed internal network includes: a kiosk including a registration module configured to read the stored software of a connected portable storage medium, a vaccine module configured to detect malicious code in the software, and an authentication module configured to set inspection authentication for the portable storage medium whose software has been inspected for malicious code; and a client including a check module configured to check the portable storage medium for inspection authentication and authorize the execution of the stored software.