Who is responsible for ensuring the security of a system throughout its lifecycle?

The responsibility for ensuring the security of a system throughout its lifecycle primarily falls on the System Owner. This individual has the overarching authority and accountability for the system, which includes not only its initial development and deployment but also ongoing maintenance and security throughout its operational life. The System Owner is involved in making decisions about security requirements, risk management, and compliance with security policies and regulations.

Throughout the system's lifecycle, the System Owner must collaborate with various stakeholders, including security officers and IT support teams, to ensure that security measures are implemented, monitored, and updated as necessary. This includes taking an active role in risk assessments, responding to security incidents, and ensuring that the system adheres to organizational security standards and best practices.

While other roles like the Security Officer or Chief Information Security Officer (CISO) have critical security responsibilities and oversight in their respective areas, it is the System Owner who holds the primary responsibility for the security of that particular system from inception through to decommissioning. Therefore, the correct answer reflects the role that encompasses the comprehensive oversight needed for system security throughout the entire lifecycle.