A DoS (Denial of Service) attack is a malicious attempt to disrupt the normal functioning of a network, system, or service by overwhelming it with a flood of traffic, data, or requests. The goal of a DoS attack is to make the targeted system or network unavailable to its intended users, thereby denying access to legitimate users.

Here are some key characteristics of DoS attacks:

Traffic Overload: The attacker floods the target system with a high volume of traffic, which could be in the form of network requests, data packets, or connection attempts. This excessive traffic can consume the system's resources, such as bandwidth, CPU, memory, or network connections, making it slow or unresponsive.
Resource Depletion: DoS attacks can exhaust critical resources, rendering the target system incapable of serving legitimate users. For example, a network-based DoS attack can consume all available bandwidth, preventing genuine traffic from getting through.
Variants: DoS attacks come in various forms, including the more aggressive Distributed Denial of Service (DDoS) attacks. In DDoS attacks, a large number of compromised computers (often a botnet) are used to collectively attack the target, making it even more challenging to mitigate.
Common Attack Techniques: Some common techniques used in DoS attacks include SYN flooding (overwhelming a server with connection requests), UDP flooding (flooding a server with UDP packets), ping flooding (sending a massive number of ping requests), and HTTP flooding (overloading a web server with HTTP requests).
Impact: The primary impact of a DoS attack is the unavailability of the targeted service, which can result in financial losses, reputation damage, and operational disruptions for the victim organization. It can also be used as a distraction tactic to divert attention from other cyberattacks.
Legality: DoS attacks are illegal in many jurisdictions because they cause harm to computer systems and networks. Perpetrators can face criminal charges and severe penalties if caught.

It's important to note that there are legitimate and responsible ways to perform stress testing or load testing on systems to evaluate their performance and resilience. These activities are performed with permission to ensure that systems can handle high loads without causing harm or disruption. In contrast, DoS attacks are unauthorized, malicious, and intended to cause harm or inconvenience.