Which of the following actions qualifies as a "security incident"?

A "security incident" refers to any event that compromises the confidentiality, integrity, or availability of information or information systems. In this context, unauthorized data access is a clear example of a security incident because it directly involves someone gaining access to data without proper authorization. This not only poses a potential risk to sensitive information but also might indicate deeper vulnerabilities in security protocols that need to be addressed.

The other actions listed, while they are important for maintaining overall security posture, do not, in themselves, constitute a security incident. Regular maintenance of IT systems is a proactive measure aimed at preventing security incidents; ensuring frequent password changes is a best practice for security hygiene but does not represent an incident; and providing training on data security is essential for awareness and prevention but again does not describe an incident. Therefore, unauthorized data access stands out clearly as the only option that reflects a breach or compromise related to security.