# Threat Classification Most attacks can be categorized as one of three broad classes: * **Intrusion**: attacks meant to breach security and gain unauthorized access to a system * **Blocking**: attacks designed to prevent legitimate access to a system * **Malware**: attacks to install malware on a system ### Intrusion Intruding onto a system without permission, usually with malicious intent, colloquially called hacking, is known as cracking. Any attack designed to breach security, either via some operating system flaw or any other means, can be classified as cracking. Includes security flaws, social engineering, war driving . ### Blocking/Denial of Service A ‘denial-of-service’ attack is characterised by an explicit attempt by attackers to prevent legitimate users of a service from using that service. One often-used blocking method is flooding the targeted system with so many false connection requests that it cannot respond to legitimate requests. DoS is an extremely common attack method. ### Malware Malware is probably the most common threat to any system, including home users’ systems, small networks, and large enterprise wide-area networks. **Virus**: a program that can ‘infect’ other programs by modifying them to include a possibly evolved copy of itself **Trojan**: a benign-looking program that can be freely downloaded but contains some virus or other malware **Spyware**: software that keeps track of what you do on your computer, e.g. a keylogger, periodic screenshots, something that saves cookies or browsing history. Data is stored for later retrieval or immediately sent through email or such. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://wiki.zacheller.dev/network-security/courses/isci-cnss-course/introduction/threat-classification.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.