Providing a framework for securing a Linux environment, this is a guide for network administrators who either have a Linux server already running or have been given the task of setting one up. Securing a Linux computer is covered, as is diagnosing and investigating intrusions and network anomalies using open source software. The basics of host security, network security, firewalls, and intrusion detection are discussed for Windows security administrators whether they are securing a single computer or an entire network of Linux computers.