Industrial Cybersecurity & OT Risk calculator
Legacy OS Risk Score Calculator
Use this calculator to score relative risk from legacy operating systems in OT. It supports defensive planning for upgrade, isolation, backup, monitoring, and compensating controls on systems that may be difficult to patch.
What this calculator does
- Rank risk from legacy operating systems in OT using impact, exposure, and compensating control weakness.
- Use it when prioritizing unsupported HMIs, engineering stations, historians, and SCADA servers for upgrade or isolation.
- The result gives a relative legacy OS risk score for prioritization.
Formula used
- Legacy OS risk score = legacy OS impact score × legacy OS exposure score × compensating control weakness score
- Use the same scoring scale across comparable legacy OS assets.
Inputs explained
- Legacy OS impact score: Score consequence if the legacy system disrupts production, safety adjacent workflows, quality, utilities, or recovery.
- Legacy OS exposure score: Score exposure based on network connectivity, remote access, user interaction, vulnerability backlog, and patch limitations.
- Compensating control weakness score: Score weakness in segmentation, application control, backups, monitoring, access control, and replacement planning.
How to use the result
- Use it to plan upgrades, isolation, monitoring, backup validation, and compensating controls.
- It does not require unsafe patching or unsupported changes to production systems.
Common questions
- What is the legacy OS risk score calculator for? It ranks risk from unsupported or difficult to patch operating systems in OT.
- What information should I enter? Use impact, exposure, and compensating control weakness scores.
- What does the result tell me? The result helps prioritize legacy system upgrade, isolation, or monitoring work.
- When is the result only an estimate? It is only an estimate when asset criticality, vendor support, or control evidence changes.
Last reviewed 2026-05-12.