IP spoofing and Denial of Service (DoS) has become the most important security threat faced by the Internet community today. One of the effective methods of defending against the types of attack is to efficiently locate its source(s). To locate the packet source, a 16-bit hybrid trace back method has been proposed. It uses both the marking and logging methods along with efficient storage method to achieve zero false positive and zero false negative rates. Furthermore, the evaluation of the proposed method on the basis of efficiency of trace back shows that it performs much better than the existing method.