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Denial of Service Attacks (DoS attacks) are a set of attacks designed to prohibit users from accessing any given network based resource. It starts with a "master machine" (the attacker's machine), which delivers a Trojan to the "slave" machine. This Trojan is a tiny, easy to hide program poised to launch DoS attacks to an intended target.

Now imagine thousands, possibly hundreds of thousands of these Trojans infecting networked machines with a Web front end, then at the command of the attacker, hundreds of these "slaves" fire a load of 800 Megabytes to one gigabyte per second at specified targets. These masses of data rocket through a string of ISPs and onto the target where they overwhelm the routers, clog the pipes, and render the servers useless. Each of the organizations along this chain - the "slave," the ISP, and the victim - hold some culpability for lax security that helped make these attacks successful.

Who commits DoS, attacks and why? Some attacks are just people testing their tools they have downloaded and are not aware of the damage they can cause. Some do it because they might not like the color scheme used on a website and attack the site for no real reason. Some people are paid to do it; for example a company might pay a hacker to make an attack on a site to delay the launch of an online business, or to discredit it. Some people may do it for fun. For example, on IRC (Internet Relay Chat) people might just be chatting in a chat room and saw someone and thought they would have a little fun so nuked or flooded them. You may have been the victim of a DoS attack on IRC yourself. Sometime you may have been chatting to your friends online then suddenly you got disconnected from the server. This could have been someone making an attack on you. DoS attacks don’t always cause a lot of damage but just disconnect you.

Computers cannot distinguish the bad guys from good guys, so it’s up to user to set up protection, rules, and filters. But you can never be too safe so you should try to get all the protection you can. How can you tell if someone's attacking you, and how can you block their attacks? There are several detectors available for windows based operating systems that monitor ports that are commonly the target of DoS attacks, and notify you when it detects a potential attack. It is also useful to be behind a firewall or a proxy server, they help protect you from attacks, and help hide your true IP from the hackers. To protect yourself more you could:
Make sure you have the current browser and operating and system patches, try closing unused UDP, TCP and FTP ports and since Trojans are often downloaded in email attachments, try not opening any .exe attachments.

If you have been a victim of a DoS attack, and if you supply all the necessary information to your ISP (Internet Service Provider), they can find out who was the physical attacker, and take legal action against them. So what information do you need to report someone? To correctly identify who was the originator of the attack, some basic information is required from the attacked user. For this purpose the various shields can be used, which has the facility to LOG all necessary information, which can then be passed to your ISP.

One of the most important things, which people sometimes don't realize is to ensure the correct time on your system. This information is necessary to correctly match the username with the IP address used at that time. The best thing is to keep your system time synchronized.