The term VPN has been associated in the past with such remote connectivity services as the public telephone network and Frame Relay PVCs, but has finally settled in as being synonymous with IP-based data networking. Before this concept surfaced, large corporations had expended considerable resources to set up complex private networks, now commonly called Intranets. These networks were installed using costly leased line services, Frame Relay, and ATM to incorporate remote users. For the smaller sites and mobile workers on the remote end, companies supplemented their networks with remote access servers or ISDN. At the same time, the small- to medium-sized enterprises (SMEs), who could not afford dedicated leased lines, were relegated to low-speed switched services.

If you have been using the Internet for any length of time, and especially if you work at a larger company and browse the Web while you are at work, you have probably heard the term firewall used. For example, you often hear people in companies say things like, "I can't use that site because they won't let it through the firewall."

Every day, the citizens of the Internet send each other billions of e-mail messages. If you are online a lot, you yourself may send a dozen or more e-mails each day without even thinking about it. Obviously, e-mail has become an extremely popular communication tool. Have you ever wondered how e-mail gets from your desktop to a friend halfway around the world? What is a POP3 server, and how does it hold your mail? The answers may surprise you,
because it turns out that e-mail is an incredibly simple system at its core! In this article, we'll take an in-depth look at e-mail and how it works!

Intrusion detection systems (IDSs) are software or hardware systems that automate the process of monitoring the events occurring in a computer system or network, analyzing them for signs of security problems. As network attacks have increased in number and severity over the past few years, intrusion detection systems have become a necessary
addition to the security infrastructure of most organizations. This guidance document is intended as a primer in intrusion detection, developed for those who need to understand what security goals intrusion detection mechanisms serve, how to select and configure intrusion detection systems for their specific system and network environments, how to manage the output of intrusion detection systems, and how to integrate intrusion detection functions with the rest of the organizational security infrastructure. References to other information sources are also provided for the reader who requires specialized or more detailed advice on specific intrusion detection issues.

Computer viruses are mysterious and grab our attention. On the one hand, viruses show us how vulnerable we are. A properly engineered virus can have an amazing effect on the worldwide Internet. On the other hand, they show how sophisticated and interconnected human beings have become. For example, MSBlaster worm and the SoBig virus. The Melissa virus - which became a global phenomenon in March 1999 -- was so powerful that it forced Microsoft and a
number of other very large companies to completely turn off their e-mail systems until the virus could be contained.