Denial of service attack

Most common type of Denial of Service attack involves flooding the target resource with external communication requests. This overload prevents the resource from responding to legitimate traffic, or slows its response so significantly that it is rendered effectively unavailable.

Resources targeted in a DoS attack can be a specific computer, a port or service on the targeted system, an entire network, a component of a given network any system component. DoS attacks may also target human-system communications (e.g. disabling an alarm or printer), or human-response systems (e.g. disabling an important technician’s phone or laptop).

DoS attacks can also target tangible system resources, such as computational resources (bandwidth, disk space, processor time),configuration information (routing information, etc.), state information (for example, unsolicited TCP session resetting). Moreover a DoS attack can be designed to execute malware that maxes out the processor, preventing usage, trigger errors in machine microcode or sequencing of instructions, forcing the computer into an unstable state, exploit operating system vulnerabilities to sap system resources, crash the operating system altogether.

The overriding similarity in these examples is that, as a result of the successful Denial of Service attack, the system in question does not respond as before, and service is either denied or severly limited.

DoS attacks are low-cost, and difficult to counter without the right tools. This makes them highly-popular even for people with technical knowledge. In fact, DoS services are offered on some web sites starting at $50. These services have grown more and more sophisticated, and can effectively exploit application vulnerabilities and evade detection by firewalls.

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

The most common and obvious type of DoS attack occurs when an attacker “floods” a network with information. When you type a URL for a particular website into your browser, you are sending a request to that site’s computer server to view the page. The server can only process a certain number of requests at once, so if an attacker overloads the server with requests, it can’t process your request. This is a “denial of service” because you can’t access that 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.