Network intrusion detection system

A network intrusion detection system, for detecting and monitoring network packets, comprising:

• a network connection unit, for receiving a plurality of network packets from a client or sending the network packets to the client;
• a storage unit, for storing the received network packets, an alert correlation program, a resource monitoring program, a plurality of detection rules, and a plurality of operation policies, wherein the network packets are detected according to the detection rules, and the network packets conforming to the detection rules are sent to the alert correlation program for analysis, a corresponding resource consumption level and a priority is assigned to each of the detection rules, and the detection rules are categorized into the corresponding operation policies according to the different resource consumption levels;
• and
• a processing unit, electrically connected to the network connection unit and the storage unit, wherein the processing unit decides whether to operate the detection rules according to the following steps:
• obtaining an device loading of the processing unit and an access load of the network connection unit by the resource monitoring program;
• deciding a loading level of the processing unit according to the device load and the access load;
• and
• operating the corresponding operation policies to detect the network packets according to the current load level, and deciding to operate the alert correlation program on each of the network packets.