In some ways, DOS attacks are like heavy storms that overload gutters. As more rainwater falls into the gutter system than it can handle, water backs up, unable to flow through until the rain lets up.
The design of the Internet Protocol technology permits the mounting of denial-of-service attacks. Denial-of-service attacks compromise the availability of computer resources.
There are two types of denial-of-service attacks. The first type of attack attempts to damage or destroy computer resources. The second type of attack overloads some system service or exhausts some resource, thus preventing others from using that service.
Denial-of-service attacks are very common on the Internet. Malicious attackers shut down websites, rebootcomputers, or clog networks with junk packets. DOS attacks can be very serious, especially when the attacker is clever enough to launch an ongoing, untraceable attack. Websites serious about security can launch these same attacks against themselves to determine how much damage can be done.
Since the sender is not interested in return traffic, it usually fakes the source addresses in its packets, making it much harder to identify the source of the attack.