You work as a Network Administrator for a bank. For securing the bank's network, you configure a firewall and an IDS. In spite of these security measures, intruders are able to attack the network…

A false positive is when the IDS generates an alarm for legitimate traffic that is not actually an attack, which is the opposite of what is described here.

A true negative is when the IDS correctly identifies that no attack is occurring and generates no alarm, which would represent accurate and expected behavior.

A true positive is when the IDS correctly detects a real attack and generates an appropriate alarm, which is exactly what the misconfigured IDS in this scenario failed to do.

A false negative occurs when the IDS does not detect or alert on a real intrusion that is actually taking place. In this scenario, intruders successfully attacked the network while the misconfigured IDS remained silent, which is the definition of a false negative. This is considered the most dangerous IDS failure mode because attacks go entirely unnoticed.