Network access and computer security work at cross-purposes. Attaching a computer to a network increases the security risks for that computer. Evaluate your security needs to determine what must be protected and how vigorously it must be protected. Develop a written site security policy that defines your procedures and documents the security duties and responsibilities of employees at all levels.
Network security is essentially good system security. Good user authentication, effective system monitoring, and well-trained system administrators provide the best security. Tools are available to help with these tasks. SSH, OPIE, Tripwire, OpenSSL, iptables, TCP wrappers, encryption, and firewalls are all tools that can help.