The Covid-19 pandemic, by reducing physical exchanges, led to unprecedented peaks in digital usage and data security breaches. The Internet of Things, big data, mobility and teleworking amplify the risks in terms of cybersecurity. Healthcare and Defense present similarities in terms of constraints and digital uses, including the need to ensure the reliability and confidentiality of data. Through a transversal approach (cognitive, social, technical, ethical and legal issues) to security, from design to use, our objective is to demonstrate the value of considering man as a full-fledged member of a complex system that must adapt to its vulnerabilities in order to increase the security and resilience of systems. Recommendations to better integrate human factors from the design stage will be proposed as well as a targeted immersive educational program to help change user behaviors.