What Is Denial Of Service (DoS) Attack - Distributed Prevent Atack

What is a denial-of-service (DoS) attack?

In a denial-of-service attack, an attacker attempts to prevent users from accessing services or information. By targeting your server and its network connection, or the servers and network of the web sites you are trying to use, an attacker may be able to prevent you from accessing email, web sites, online accounts (banking, etc.), or other services that rely on the affected server.

The most commonly and obvious type of denial-of-service attack happens when an attacker "floods" a network with information. When you type a URL for a web site into your browser, you are sending a request to that web site's server to view the page. The server can only process a certain number of requests at once, therefore, if an attacker overloads the server with requests, it cannot process your request. This is a "Denial-of-Service" because you cannot access that web site.

An attacker can use spam email messages to launch a similar attack on your email account. Whether you have an email account supplied by your employer or one available through a free service such as Yahoo or Hotmail, you are assigned a specific quota, which limits the amount of data you can have in your account at any given time. By sending many, or large, email messages to the account, an attacker can consume your quota, preventing you from receiving legitimate messages.
What is a distributed denial-of-service (DDoS) attack?
In a distributed denial-of-service (DDoS) attack, an attacker may use your server to attack another server. By taking advantage of security vulnerabilities or weaknesses, an attacker could take control of your server. He or she could then force your server to send huge amounts of data to a web site or send spam to particular email addresses. The attack is "distributed" because the attacker is using multiple servers, including yours, to launch the denial-of-service attack.