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A distributed denial-of-service (DDoS) is a type of computer attack that uses a number of hosts to overwhelm a server, causing a website to experience a complete system crash. This type of denial-of-service attack is perpetrated by hackers to target large-scale, far-reaching and popular websites in an effort to disable them, either temporarily or permanently. This is often done by bombarding the targeted server with information requests, which disables the main system and prevents it from operating. This leaves the site's users unable to access the targeted website.
DDoS differs from a denial-of-service (DoS) attack in that it uses several hosts to bombard a server, whereas in a DoS attack, a single host is used.
In a standard DDoS attack, an attacker starts the process by taking advantage of a vulnerability in a computer system. The hacker makes this compromised computer the DDoS master. Using this master system, the hacker detects, communicates and infects other systems and makes them a part of the compromised systems. A compromised computer system within the control of a hacker is called a zombie or bot, while a set of compromised computers is called a zombie army or a botnet. The hacker loads several cracking tools on the compromised systems (sometimes thousands of systems). Using a single command, the attacker instructs these zombie machines to trigger several flood attacks toward a particular target. This packet flooding process causes a denial of service.
In a DDoS attack, the victim is not only the final target; all the compromised systems are victims of this kind of attack.
WordPress.com, an open-source electronic publisher accessed by millions of electronic publishers and even more electronic authors for content publishing standards, experienced a major DDoS in March 2011. The attack is believed to have been a politically motivated attack against one of the blogs that appears on WordPress. The site was reportedly down for up to three hours, although users report that it had been extremely slow in the days leading up the crash. The size of the crash pointed to the use of botnets to perpetrate it.