The present invention relates to a network intrusion detection and prevention system. The system includes: a signature based detecting device; an anomaly behavior based detecting device; and a new signature creating and verifying device disposed between the signature based detecting device and the anomaly behavior based detecting device, wherein if the anomaly behavior based detecting device detects network-attack-suspicious packets, the new signature creating and verifying device collects and searches the detected suspicious packets for common information, and then creates a new signature on the basis of the searched common information and at the same time, verifies whether or not the created new signature is applicable to the signature based detecting device, and then registers the created new signature to the signature based detecting device if it is determined that the created new signature is applicable.