Segmentationis the best option to ensure the security of legacy badge readers that cannot be upgraded. Segmentation isolates the legacy devices on a separate network segment to minimize their exposure to potential threats. This approach reduces the attack surface by preventing unauthorized access from other parts of the network while still allowing necessary connectivity to the enterprise resource planning (ERP) system.

Vulnerability scans (B)are useful for identifying weaknesses but do not actively protect the badge readers.

Anti-malware (C)is ineffective since the badge readers use a legacy platform that likely does not support modern endpoint protection solutions.