Pin Me

What is a Denial-of-Service Attack?

written by: Mark Muller•edited by: Bill Bunter•updated: 2/25/2011

In this article you will find all you want to know about denial-of-service (DoS) attacks and distributed DoS (DDoS) attacks. Read on here to find a definition of denial-of-service attack and much more including the latest denial-of-service developments: ‘smart’(DoS) attacks!

  • slide 1 of 1

    Any attempt to deliberately make a legitimate computer service or web site unavailable is called a denial-of-service attack. In contrast to viruses and malware does a denial-of-service (DoS) attack not require an infection or any other action on behalf of the victim computer. Neither does a DoS attack make changes to files or properties of the server being attacked. Rather, the DoS attack tries to stop a computer service such as an ecommerce (web) site from functioning as designed by making the service temporarily unavailable. This is achieved by flooding the server with more requests than the web server can handle; thus, the DoS attack is carried out by one or more Internet connected computers over the TCP/IP protocol stack. In consequence, a user who wants to make use of a service such as browsing the attacked website for online shopping will experience a huge lag (degradation of service) or receive a browser/http time-out error (denial of service).

    A DoS attack is likely to be noticed fast and action taken swiftly by blocking the IP address of the computer sending an excessive amount of requests. However, there might be hundreds or thousands of computers sending bogus traffic at the same time in case of a Distributed Denial-of-Service (DDoS) attack. Most hosts participating in a DDoS attack are relatively easy identifiable, Zombies of botnet (More about Zombie computers can be found in Bright Hub’s article What is a Zombie computer?). DoS attacks not only have evolved in distributed computing but a new generation of DoS attack does also send ‘smart’ requests to hinder computer services from working properly: By sending relatively few resource heavy requests the effect will not be perceived as DoS attack but legitimate traffic all the more as globally dispersed Zombies are being used by the botnet operators cyber criminals.

    These cybercriminals sometimes demand money from their victims to stop the ongoing attack - in ecommerce every minute downtime costs money and a company’s reputation is at stake. Thus, a DoS attack has the pecuniary aim in common with ransomware. As an ordinary computer user you will unlikely become the victim of DoS attack because DoS attacks mostly aim at web servers, but it is your responsibility to do all you can so that your computer does not become a Zombie by patching your system and using capable anti-virus and anti-spyware software such as Webroot AntiVirus with AntiSpyware for example. As a best practice to protect a small business’ website or enterprise from DoS as well as degradation-of-service attacks it is recommended to include the service attack scenarios in your organizations’ incident response plan and perhaps buying a network intrusion prevention and detection system.