A DoS or Denial-of-Service attack is an attack targeting the availability of web applications. Unlike other kinds of attacks, the primary goal of a DoS attack is not to steal information but to slow or take down a web site. The attackers' motivations are diverse, ranging from simple fun, to financial gain and ideology (
). A denial of service attack generates high or slow rate attack traffic exhausting computing resources of a target, therefore preventing legitimate users from accessing the website.
Denial-of-Service/DoS attacks affect enterprises from all sectors (e-gaming, Banking, Government etc.), all sizes (mid/big enterprises) and all locations. They target the network layer and up to the application layer, where attacks are more difficult to detect since they could easily get confused with legitimate traffic.
There are several types of denial of service attacks. Non distributed DoS attacks are when an attacker uses a single machine's resources to exhaust those of another machine, in order to prevent it from functioning normally. Large Web servers are usually robust enough to withstand a basic denial of service attack from a single machine without suffering performance loss. A famous variant is the
DDoS, or Distributed Denial of Service attack
, where the attack originates from multiple computers simultaneously, therefore causing the victim's resources exhaustion.