This paper describes a technique of applying Genetic Algorithm (GA) to network security. As the transmission of data over the Internet increases, the need to protect connected systems also increases. Rule based network security is the latest technology used for this purpose. Although the field of network security is still developing, the systems that do exist are still not complete, in the sense that they are not able to detect all types of intrusions. Some attacks which are detected by various tools available today cannot be detected by other products, depending on the types and methods that they are built on. Using a Genetic Algorithm is one of the methods that detect intrusions. The focus of this paper is to introduce the application of GA, in order to improve the effectiveness of network security. Unlike other implementations of the same problem, this implementation considers both temporal and spatial information of network connections in encoding the network connection information into rules in network security. This is helpful for identification of complex anomalous behaviors. This work is focused on the TCP/IP network protocols.