Denial-of-Service Attack

Sometimes abbreviated DOS, are an outside user’s attempt to make a machine or network resource unavailable for its intended users. These attacks are often used to temporarily, or indefinitely suspend services of a host connected to the Internet. Most commonly, an outside attacker will saturate the targeted server with external requests, preventing the machine from responding to legitimate traffic or substantially slowing its response to these users. This leads to a server overload, forcing the targeted computers to restart. During this time communication media between the intended users and the attacked machine are obstructed.

Attackers commonly target high profile web servers such as banks and credit card payment gateways; this is not commonly used to target websites with relatively small audiences or those without financial transactions. Common symptoms of a denial-of-service attack include: slow network performance, including slow file access or unavailable websites, unavailable web pages on a site, or a dramatic increase in spam emails.

There are five basic denial-of-service attacks that may be employed against a targeted machine. In the first, a user will force the targeted computer to consume massive amounts of resources such as bandwidth, disk space or processor time. In the second, the attacker will disrupt the configuration of important details, such as routing information. A third common DOS is the disruption of state info, including the unsolicited resetting of TCP sessions. A fourth attack is a physical disruption of the machine or server. And a fifth, final attack, is the obstruction of communication media.