DoS attacks can be used to specifically impair the availability of a website, for example by blocking individual accounts through incorrect logins. An attacker could, for example, ensure that user accounts are blocked by invalid login attempts.

DDoS (distributed denial of service) attacks may result in the partial or total failure of a web server. In such case, users’ access to corresponding web offerings will be very slow or not available at all. For many organisations, such failures can quickly become business-critical (when they affect online shops, for example).