Final answer:
A Pattern based system, also known as Signature-based detection, would use alerts and send these if it detects traffic matching certain threat signatures. The correct answer is b.
Step-by-step explanation:
The type of logical intrusion system that would only use alerts and send the alerts if it sees traffic matching certain signatures is a Pattern based system, also known as Signature-based detection. These systems are designed to match the traffic that passes through the network against a database of known threat signatures or patterns associated with malicious activity. This method can be highly effective against known threats, but it may not recognize new, previously unknown attacks.
Dedicating a comparison to the provided options: Heuristic based systems involve using rules or algorithms to weigh the characteristics of potential threats, allowing them to detect new or unknown threats through abnormal behavior patterns. An Intrusion Prevention System (IPS) not only detects but also prevents the intrusion attempts by blocking or stopping the attack in real-time. Hence the correct option is b.