the user in a human-recognizable format and to interface with the presentation layer below it. In an implementation, the application and presentation layers are frequently combined. Method of attack The simplest DoS attack relies primarily on brute force, flooding the target with an overwhelming flux of packets, oversaturating its connection bandwidth or depleting the target's system resources. Bandwidth-saturating floods rely on the attacker's ability to generate the overwhelming flux of packets. A common way of achieving this today is via distributed denial-of-service, employing a botnet. An application layer DDoS attack is done mainly for specific targeted purposes, including disrupting transactions and access to databases. It requires fewer resources than network layer attacks but often accompanies them. An attack may be disguised to look like legitimate traffic, except it targets specific application packets or functions. The attack on the application layer can disrupt services such as the retrieval of information or search functions on a website. Advanced persistent DoS An advanced persistent DoS (APDoS) is associated with an advanced persistent threat and requires specialized DDoS mitigation. These attacks can persist for weeks; the longest continuous period noted so far lasted 38 days. This attack involved approximately 50+ petabits (50,000+ terabits) of malicious traffic. Attackers in this scenario may tactically switch between several targets to create a diversion to evade defensive DDoS countermeasures but all the while eventually concentrating the main thrust of the attack onto a single victim. In this scenario, attackers with continuous access to several very powerful network resources are capable of sustaining a prolonged campaign generating enormous levels of un-amplified DDoS traffic. APDoS attacks are characterized by: advanced reconnaissance (pre-attack OSINT and extensive decoyed scanning crafted to evade detection over long periods) tactical execution (attack with both primary and secondary victims but the focus is on primary) explicit motivation (a calculated end game/goal target) large computing capacity (access to substantial computer power and network bandwidth) simultaneous multi-threaded OSI layer attacks (sophisticated tools operating at layers 3 through 7) persistence over extended periods (combining all the above into a concerted, well-managed attack across a range of targets). Denial-of-service as a service Some vendors provide so-called booter or stresser services, which have simple web-based front ends, and accept payment over the web. Marketed and promoted as stress-testing tools, they can be used to perform unauthorized denial-of-service attacks, and allow technically unsophisticated attackers access to sophisticated attack tools. Usually powered by