Network security is a part of computer networking that ensures that the network is totally secure. It takes care that both hardware and the software in the network are fully protected against any unauthorized access. The network security is handled by the network administrator or the system administrator. The operators working on the network system should be given sufficient access so that they must be able to do their assigned tasks. Full access is not given to the operators. This prevents them to focus on their work only and not on illegal modification of the computer resources. Computer networks may be private or public. When the network allows access to only some limited users, it is a private computer network. On the other hand, when the access is to the general public also, it is a public network. In a public network security demands are high. As the users are unlimited, the networks should have firewalls, which are a type of network security to prevent damage to the computer network system.