What may indicate a security incident?

The correct choice highlights the fact that security incidents can often manifest through less obvious signs rather than a clear assault on the system. Indicators of a security incident can be subtle, such as unusual network activity, unexpected changes in system performance, or even application anomalies. This underscores the importance of being vigilant and monitoring for signs that something may not be functioning as expected.

The other options do not fully capture the nature of security incidents. Visible alerts can certainly signal a potential issue, but they aren't always present during an incident. It's also not always clear when an attack occurs, as threats can develop quietly over time. Lastly, while physical damage to equipment can be an indication of a security incident, it is more specific and not as broadly applicable as the indicators mentioned in the correct answer. Recognition of only indicators is essential in ensuring that potential threats are addressed before they escalate into more significant incidents.