When a number of systems i.e. one or more than one web server floods the resources and bandwidth of a targeted system then a distributed denial of service attack (DDoS) takes place, Different types of methods are used by attackers in order to compromise the systems.
It is the malware that can carry out the mechanisms of DDoS attack; its best example was MyDoom. The mechanism of its DoS was actually triggered on a specific time and date. The DDoS of this kind involves hardcoding of the target IP address before the release of malware and there was no need of communication for launching the attack.
It can also happen that the system may be compromised with a trojan, giving a permission to the attacker downloading a zombie agent (sometimes the trojan already contain one). Attackers can destroy the systems with the help of automated tools that exploit the faults present in programs and listen for connections from far away hosts. The primary concern of this scenario is that the systems start serving as web servers.
One of the classic examples of DDoS tool is Stacheldraht DDoS tool. A layered structure is used and the attacker make use of a client program for connecting to the handlers, and these are compromised systems that send commands to the zombie agents, which give rise to DDoS attack. The handlers can control the agents with the use of automated routines in order to exploit program’s vulnerabilities that accept the connections running far away on the targeted hosts. Every single handler has a capacity to control up to 1000 agents.
These systems compromisers are referred to as botnets. Still the DoS tools like Stacheldraht utilizes the classic method of DoS attack centered on IP spoofing as well as amplification like fraggle attacks and smurf attacks (also referred to as bandwidth consumption attacks). Sometimes the SYN floods or resource starvation attacks may be used too. For the purpose of DoS modern tools can utilize DNS servers.
