Anyone who administers a system connected to the Internet needs to know something about network security. It's not uncommon for systems connected to the Internet to be probed by would-be hackers several times daily. If a would-be hacker manages to detect a vulnerability, the hacker can often exploit it in a matter of seconds. Therefore, it's almost certain that a system administrator ignorant of network security will eventually suffer a system break-in.
Network security is a large and sophisticated topic that can be only cursorily surveyed in a book such as this. Concerned readers should consult books such as Building Internet Firewalls, by Elizabeth D. Zwicky, Simon Cooper, and D. Brent Chapman (O'Reilly & Associates, Inc.); Computer Security Basics, by Deborah Russell and G.T. Gangemi, Sr. (O'Reilly); and Practical Unix & Internet Security, by Simson Garfinkel and Gene Spafford (O'Reilly).
If a sufficiently skilled hacker is intent on compromising a system you administer, the hacker will probably succeed. However, here are some tips that can help you avoid falling victim to amateur hackers:
Establish a firewall that prevents outsiders from accessing services you don't need to make publicly available.
Monitor security web sites and mailing lists so that you're aware of recent threats and the associated countermeasures. The CERT Coordination Center, http://www.cert.org, provides many useful resources.
Apply bug fixes promptly, particularly those related to security. See Red Hat's errata page, http://www.redhat.com/support/errata/rh8-errata.html, for applicable fixes. To be informed of Red Hat Linux fixes when they're released, subscribe to Red Hat Network or the redhat-watch-list email list. To subscribe to Red Hat Network, visit http://rhn.redhat.com. To subscribe to the email list, visit https://listman.redhat.com/mailman/listinfo/.