DoS attack & DDoS attack

A Denial-of-Service (DoS) attack is designed to hinder or stop the normal functioning of a web site, server or other network resource. There are various ways for hackers to achieve this. One common method is to flood a server by sending it more requests than it is able to handle. This will make the server run slower than usual (and web pages will take much longer to open), and may crash the server completely (causing all websites on the server to go down).

A distributed-Denial-of-Service (DDoS) attack differs only in the fact that the attack is conducted using multiple machines. The hacker typically uses one compromised machine as the ‘master’ and co-ordinates the attack across other, so-called ‘zombie’, machines. Both master and zombie machines are typically compromised by exploiting a vulnerability in an application on the computer, to install a Trojan or other piece of malicious code.