DOS-attack

Its Real,On February 6th, 2000, Yahoo portal was shut down for 3 hours. Then retailer Buy.com Inc. (BUYX) was hit the next day, hours after going public. By that evening, eBay (EBAY), Amazon.com (AMZN), and CNN (TWX) had gone dark. And in the morning, the mayhem continued with online broker E*Trade (EGRP) and others having traffic to their sites virtually choked off.

What is a Denial Of Service Attack?



A denial of service attack (DOS) is an attack through which a person can render a system unusable or significantly slow down the system for legitimate users by overloading the resources, so that no one can access it.
If an attacker is unable to gain access to a machine, the attacker most probably will just crash the machine to accomplish a denial of service attack.
Types of denial of service attacks

There are several general categories of DoS attacks.Popularly, the attacks are divided into three classes:

bandwidth attacks,
protocol attacks, and
logic attacks

What is Distributed Denial of Service Attack?

An attacker launches the attack using several machines. In this case, an attacker breaks into several machines, or coordinates with several zombies to launch an attack against a target or network at the same time.
This makes it difficult to detect because attacks originate from several IP addresses.
If a single IP address is attacking a company, it can block that address at its firewall. If it is 30000 this is extremely difficult.