Denial of Service Attacks
A "Denial of Service (DoS) attack" broadly refers to an attacker causing an important resource or service to become unavailable to its regular user base. In the cyber world, a DoS means normal network operations, such as e-mail and Internet access, become unavailable.
In its worst form, a DoS attack can force a website to shut down its regular operation. It can also destroy files and programming housed within a network.
Although DoS attacks are usually intentional and malicious, it is possible for a DoS to be purely accidental. Whatever the cause, one thing is certain—a DoS attack can cause its target, be it an individual user or a business, to lose a significant amount of time and money.
A DoS may be executed a number of ways, both digitally and physically. A very simple DoS might be merely cutting a fiber optic cable at an Internet Service Provider, thus denying service to its customers.
The CERT® Coordination Center offers information on how to prevent denial of service attacks.
Distributed Denial of Service Attacks
A Distributed Denial of Service (DDoS) attack is when an attacker compromises several computer systems and uses them to attack a specific target. The more systems that are used as tools, the more traffic can be sent to the targeting network, and the greater the chances of shutting that system down.
To pull off a DDoS, an attacker first exploits the security vulnerabilities in one computer system, and then goes on to exploit systems, making them "zombies." The number of zombies range from two to as many as several thousand. The attacker then commands the zombies to launch an attack against a single targeted system, causing a massive denial of service.
A distributed denial of service attack is especially severe because it victimizes not only the targeted systems, but each of the "slave" systems as well.
"Barbarians at the Gate: An Introduction to Distributed Denial of Service Attacks," is an in-depth article exploring DDoS attacks, written by Matt Tanase.
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