
The purpose, target websites and the way the attack is carried out may vary.
However, every attack always comprises of attempts to indefinitely or temporarily suspend or interrupt services provided by a host which is connected to the internet.
DOS attack perpetrators usually target those sites and/or services which are hosted on high-profile web servers like credit card payment gateways, banks and even the root nameservers.
The technique finds an extensive use in certain games which are used by peeved competitors on games or server owners.
DoS attack is also being increasingly used as a form of resistance.
Any DDOS attack whether it is inbound if you are victimized to attack or outbound if you are the culprit, directly violates Accepted Use Policy of all recognized and reputed web hosting service providers.