Denial of Service (“DOS”) attacks are a system of spamming your systems in such manner as to deprive the owner of a computer system or its users, access to such computer system and through such denial of access the purpose of such system is defeated.

If a website expects traffic of about 200,000 users. Instead on a single day 20,00,000 users land on the website. Beyond its expected capacity that it has provisioned for which could be 200,000 or may be a margin of 300,000, the website will not be able to sustain this surge in additional traffic. It is like a corner shop which always expects about 10 – 20 customers at a given time getting crowded with a 1000 customers trying to squeeze themselves in. With the additional crowd of 1000 customers ganging up and blocking the shop, the regular customers the shop has will not be able to enter. This will not only cause loss to the shopkeeper for a day but could make him lose his customers forever. In similar fashion, when the website’s genuine customers or users cannot access the site because of the bombardment, it denies them access to an infrastructure meant for genuine users. This is the reason for this simple description of a crime, which can cause grave harm.

The above illustration is very simplistic and describes a basic DOS attack. However entire nations and their critical infrastructure can be affected injuriously or brought down completely with such attacks.