The problem of performing cybersecurity tests over existing industrial control systems is well-known. Once it is deployed, a critical system cannot be made unavailable for the purpose of simulating a cyber attack and thus it is hard to introduce corrective measures based on actual test outcomes. On the other hand, a high security posture is required for critical infrastructure and security by design is mandatory for new projects. Such requirements call for an architectural approach to introduce security straight from the early development phases. However, the adoption of a systematic design approach does not guarantee the cost-effectiveness of security countermeasures analysis, which is an extremely cumbersome task as the creation of a physical model is often costly or impossible.To address these issues, we propose the introduction of a specific view in the system’s architectural blueprint, called the Cybersecurity Digital Twin. It is an Enterprise Architecture model of the system specifically targeted at providing a sound base for simulations in order to devise proper countermeasures without any outage of the physical infrastructure. To provide a proof of concept and demonstrate the practical viability of the proposed solution, we apply the methodology to a Cooperative Intelligent Transport System use case, evaluating the system security of the obtained solution.