In the context of Intrusion Detection Systems (IDS), determining whether an event is a True Negative, True Positive, False Negative, or False Positive depends on the system's detection and the reality of the situation.

Let's break down the scenario:

IDS Signature Explanation:

The IDS is set to detect and alert on logins to a server, but only if they happen during a specific time window, from 6:00 PM to 6:00 AM.

The question states that no alerts occur during this time frame, but the IDS signature is known to be correct.

Understanding Detection Terms:

True Positive: The IDS correctly detects an intrusion or suspicious activity that is actually happening.

True Negative: The IDS does not detect any activity because no suspicious or malicious activity is occurring, and this lack of detection is correct.

False Positive: The IDS detects an intrusion or activity, but it is a false alarm (i.e., there is no real threat).

False Negative: The IDS fails to detect a real intrusion or activity when it should have, missing a legitimate alert.

Applying the Scenario:

In this case, no IDS alerts occurred during the specified time frame. If there were no actual logins during this period and the signature was designed correctly, then the absence of alerts is expected and appropriate.

Since no suspicious logins occurred, and the IDS did not trigger any alerts, this situation represents a True Negative—the system correctly identified that there was no suspicious activity to alert on.

Why the Answer is "True Negative":

The IDS signature is working as expected.

The condition that would trigger an alert (logins during the specified time) did not happen, so the lack of alerts is a correct response.

Therefore, this is classified as a True Negative because no malicious activity took place, and the IDS correctly refrained from raising an alert.

Comparison to Other Options:

B. True Positive – This would indicate that an alert occurred because of actual suspicious activity, but in this case, no alerts occurred.

C. False Negative – This would mean that suspicious activity occurred, but the IDS failed to detect it. In this case, there was no activity to detect, so this option is not correct.

D. False Positive – This would suggest the IDS raised an alert when no suspicious activity happened, but again, no alerts occurred, so this doesn’t apply.

References:

Cybersecurity analysts working with IDS systems frequently use concepts like True Negative and False Positive in evaluating the effectiveness of their detection tools.

The correct handling of such detection cases is critical to minimizing unnecessary alerts (False Positives) and ensuring real threats are not missed (avoiding False Negatives).