The end goal of the Denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is to make a resource unavailable to its users. The attack can be carried out on different levels, depending on the target and the people involved. In essence, the attack represents a highly intense attempt by one person or more to hinder websites or specialized internet services from running properly, causing financial losses to that resource's owner.

Depending on the motivation behind the attack, different targets might suffer from it. The attack can be implemented by a single person, carrying out a personal agenda. Such an attack is improbable to cause too much trouble and will only be temporary. A much bigger problem is organized attacks performed by a group of individuals in pursuit of financial gains. Such attacks can be sustained for longer periods of time and might as well ruin companies relying on online presence. Banks, online retailers, government sites, payment gateways, and even root nameservers can become easy prey for organized DDoS attacks.

The most common attack method involves flooding the website (and web server along with it) with external communications requests to such a level that it cannot respond to legitimate traffic generated by regular users. Needless to say, precious business is driven away. Their hosting provider might sometimes force unprotected parties to move their website to different hosting because the attack intended to render one site unusable prevents the whole web server (thousands or tens of thousands of sites) from delivering their content to visitors.

Saboteurs are usually after a hefty ransom, threatening to continue the attack for as long as they have to unless the amount is paid. Such people are considered outlaws and are threatened by up to 10 years in prison, depending on local law.

There are ways to protect your online business from such attacks, and usually, it is best to be proactive. Wikipedia.org and Cisco.com are two good points to start from, should you be interested in learning more about prevention and actions you might take. If you are the proud owner of a small website with a modest amount of traffic, you shouldn't be too worried about the DDoS attack. That does not mean you can't monitor your website or server. For as low as 9$ per month, you can be aware of whether your site is a victim of malevolent attacks.