A tool called nmap is generally considered the best way to scan a host for services (note
that nmap is a tool that can be used for good and evil). Once the attacker has a list of the
available services running on his target, he or she needs to find a way to trick one of those
services into letting him or her have privileged access to the system. Usually, this is done
with a program called an exploit.
While DOS attacks are disruptive, intrusion attacks are the most damaging. The reasons are varied,
but the result is always the same. An uninvited guest is now taking up residence on your machine
and is using it in a way you have no control over.
Protecting Against Denial of Service Attacks
As explained earlier, a Denial of Service attack attempts to crash your computer or at least degrade
its performance to an unusable level. There are a variety of Denial of Service exploits. Most try to
overload some system resource, such as your available disk space or your Internet connection.
Some common attacks and defenses are discussed in the following sections.
Mailbombing
Mailbombing is the practice of sending so much e-mail to a particular user or system that the computer??™s
hard drive becomes full. There are several ways to protect yourself from mailbombing.
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