Cyber security roadmap: Add content to empty nodes (#6314)

* Add content to siem@c2kY3wZVFKZYxMARhLIwO.md

* added content to empty nodes: smishing, tailgating, whishing(vishing), and whois

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+# SIEM
+
+SIEM, short for Security Information and Event Manager, is a term used to describe tools that greatly increases visibility into a network or system. 
+It does this by monitoring, filtering, collecting, normalizing, and correlating vast amounts of data such as logs, and neatly presents it via an interface/dashboard. 
+
+Organizations leverage SIEMs to monitor and thus identify, protect, and respond to potential threats in their environment. 
+
+For hands-on experience, you should consider setting up a SIEM in your own environment. A common stack widely used for various purposes across the industry is the ELK-stack.
+
+Visit the following resources to learn more:
+
+- [@article@Security 101: What is a SIEM? - Microsoft](https://www.microsoft.com/security/business/security-101/what-is-siem)
+- [@article@Using the ELK stack for SIEM](https://logz.io/blog/elk-siem/)
+- [@video@Build a powerful home SIEM](https://www.youtube.com/watch?v=2XLzMb9oZBI)

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+# Smishing
+
+SMS-phishing, or "smishing", is a type of social-engineering attack based on SMS, or text messages, to trick a victim into doing something to the benefit of the attacker, such as clicking on a malicious link or providing sensitive information.

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+# Tailgating
+
+Tailgating is the act of getting access to a restricted area by simply following an authorized person. This is a common social engineering technique used by attackers to gain physical access to a building or a restricted area. The attacker waits for an authorized person to open the door and then follows them inside. This technique is effective because it is based on trust and the assumption that the attacker is an authorized person.

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+# Whishing
+
+Social engineering attack involving voice, such as a phone call to trick a victim to do something to the benefit of the attacker.
+
+Derived from voice-phishing, or "vishing".

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+# Whois
+
+Whois is a protocol that allows querying databases to obtain information about the owner of a domain name, an IP address, or an autonomous system number on the Internet.
+
+In the field of cyber security, Whois data is one of several components in passive reconnaissance and open-source intelligence(OSINT) gathering.
+
+- [@article@How to use the whois command on Linux](https://www.howtogeek.com/680086/how-to-use-the-whois-command-on-linux/)
+- [@article@Whois lookup](https://www.whois.com/whois/)