A DoS or DDos attack is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connected to the Internet. Denial of service is typically accomplished by flooding the targeted machine or resource with superfluous requests in an attempt to overload systems and prevent some or all legitimate requests from being fulfilled.
DoS attacks do not typically result in the theft or loss of significant information or other assets, they can cost the victim a great deal of time and money to handle and resolve.
DoS attacks can range in duration and may target more than one site or system at a time. An attack becomes a ‘distributed denial of service’, referred to as “DDoS”, when it comes from multiple computers (or vectors) instead of just one. This is the most common form of DoS attack on websites.
Malicious attacks can take one of two general forms: Denial of Service (DoS) or Distributed Denial of Service (DDoS).
The difference between DoS and DDoS is:
- A DoS (Denial of Service) attack uses only a small number of attacking systems (possibly just one) to overload the target. This was the most common type of attack in the early days of the Internet, where services were relatively small in scale and security technology in its infancy. However, nowadays, a simple DoS attack is often simple to deflect as the attacker is easy to identify and block. One notable exception here may be industrial control systems, where equipment may have a low tolerance to bogus traffic, or may be connected via low bandwidth links that are easily saturated.
- In a DDoS (Distributed Denial of Service) attack, the attacker enlists the help of (many) thousands of Internet users to each generate a small number of requests which, added together, overload the target. These participants may either be willing accomplices (such as attacks initiated by loosely organised illegal “hactivist” groups) or by unwitting victims whose machines have been infected with malware.