The Internet has transformed greatly the improved way of business, this vast network and its associated technologies have opened the doors to an increasing number of security threats which are dangerous to networks. The first part of this chapter presents a new dimension of denial of service attacks called TCP SYN Flood attack has been witnessed for severity of damage and second part on worms which is the major threat to the internet. The TCP SYN Flood attack by means of anomaly detection and traces back the real source of the attack using Modified Efficient Packet Marking algorithm (EPM). The mechanism for detecting the smart natured camouflaging worms which is sensed by means of a technique called Modified Controlled Packet Transmission (MCPT) technique. Finally the network which is affected by these types of worms are detected and recovered by means of Modified Centralized Worm Detector (MCWD) mechanism. The Network Intrusion Detection and Prevention Systems (NIDPS) on Flooding and Worm Attacks were analyzed and presented.