What is a DoS (Denial of Service) Attack?
SUMMARY: How can your computer be hacked and turned into a tool to damage other machine via Denial of Service attacks?
A DoS (Denial of Service) attack (not to be confused with dos or DOS, which stands for Disk Operating System), is an attack whereby one computer or a group of loosely networked computers attempt to send too much information to a remote computer or server, such as a web server. A DoS floods the remote computer with so much traffic that it cannot handle normal, valid requests made from others. DoS attacks work as the remote computer cannot easily distinguish requests and traffic sent from the DoS-attacking machines versus that sent by valid means.
Two main types of DoS attacks:
*Ping Flood, whereby remote computers constantly send an "ICMP Echo Request" - an "Are You There?" signal - to a server. The server constantly acknowledges that it does exist, handling these requests so much that it effectively ignores other traffic.
*Web server flooding, sending a website so many requests that it cannot handle valid requests from other users, basically shutting it down.
DoS attacks have been done against some of the larger websites, including Microsoft, Yahoo, and SCO. Attacks sometimes are made for financial reasons, others political, and others to protest a company's actions.
If your computer gets infected with a particular type of malware called a Remote Access Trojan (RAT), you could become an unknowing participant in a DoS attack. If malicious software gains control over enough machines, it can cause those machines to send a torrent of traffic towards a remote host, in effect shutting it down. A side-effect is that as machines are themselves sending huge amounts of traffic to another machine, they in turn are less able to handle valid Internet traffic, thus the infected machines in essence are hit by self-inflicted DoS attacks.
Besides antivirus software, constant operating system and browser updates, and anti-spyware software, a good defense against your machine being used to perform a DoS attack is a hardware or software firewall. Firewall programs, in many cases, can detect whether or not unknown programs are trying to access the Internet and allow you the chance to prevent them from running. In this case, even if your computer becomes infected, a firewall can sometimes help your machine from striking out against a remote computer, reducing bandwidth use on both ends.
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