A retrofit is an upgrade added to an existing building or system to improve performance, efficiency, or compliance without replacing the whole installation. In cyber security, the term often applies to legacy facilities, industrial systems, or building automation networks that were not designed with modern defenses in mind.
Retrofits matter because old equipment is hard to rebuild from scratch, but attackers still target it through weak passwords, exposed controllers, poor network segmentation, and outdated firmware. Security retrofits can include adding monitored access control, replacing insecure devices, deploying sensors, isolating OT and IT traffic, enabling logging, and applying identity controls such as multi-factor authentication. The challenge is making these changes work safely with existing hardware and operations.