Which of the following is used to detect malicious activity such as port scans or even attempts for cracking into computers by monitoring network traffic?

IIPS is not a recognized standard security acronym and does not represent a real intrusion detection or prevention category.

NIDS (Network Intrusion Detection System) passively analyzes packets traversing the network in real time, comparing traffic patterns against known attack signatures to detect threats like port scans, DoS attempts, and brute-force logins. It operates at the network level and can monitor traffic for all hosts on a segment simultaneously, making it the correct tool for the described scenario.

PIDS is not a standard or widely recognized classification within intrusion detection systems relevant to this scenario.

HIDS (Host-based Intrusion Detection System) monitors activity on a single endpoint such as log files and system calls, not network traffic.