Final answer:
The example of a computer security incident is a former employee crashing a server. This act is a deliberate disruption to computer services, often related to data breaches and cybercrime, posing threats to an organization's information assets.
Step-by-step explanation:
Among the options provided, D. Former employee crashes a server is an example of a computer security incident. A security incident in the context of information technology generally refers to an event that violates an organization's security policies and poses a threat to its information assets. Users accessing secure files (option A) and administrators changing file permissions (option B) are both routine and authorized activities that contribute to the management of an organization's data security. These actions are only considered incidents if they are done without proper authorizations or with malicious intent.
An intruder breaking into a building (option C) is certainly a security concern, but it is primarily a physical security issue rather than a computer security incident unless the intruder gains unauthorized access to computer systems. Finally, option D indicates a deliberate act to disrupt services, which clearly falls under the umbrella of computer security incidents. It touches on areas such as data breaches, cybercrime, and unauthorized access, which have significant financial and reputational implications for businesses and individuals alike.