Chapter 1 · Computer Networks
1.14Network Security
How firewalls, encryption and access control keep a network safe, and the common threats they protect against.
Written and checked by Muhammad Raheel(opens in a new tab)
Full Stack Developer · AI Engineer · Reviewed 21 Oct 2026 · 3 min read
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Every day, many people join networks at home, at school and at work. Each of them sends and receives data. Without protection, a stranger could read that data, change it or delete it. Network security is the set of tools and rules that stops this.
"Unauthorized" means without permission. Security also helps prevent data loss and damage. It matters for homes and for organizations. It protects personal information, keeps hackers out, keeps data private and protects devices from malware (harmful software). A secure network also works smoothly, without interruptions. The book's message is simple: every network needs basic security measures.
The chapter Summary gives a second definition:
The book's class activity asks you to discuss how security protects sensitive data, such as the CT scans of patients in a hospital. Think about who should see a scan, and which of the tools below would keep everyone else out.
Firewalls
A firewall stands between your network and the outside world, like a guard at a gate. It checks traffic coming in and going out.
Harmful or unwanted data is blocked at the firewall. So the firewall acts as a barrier between safe and unsafe networks, and it protects computers from attacks. Firewalls are used in homes and offices. The book shows this in Figure 1.17, "Firewall Protection".
Encryption
Encryption hides the meaning of data while it travels.
If someone catches encrypted data on the way, they see only meaningless symbols. That is why encryption protects data during transfer and helps prevent data theft. The book names two places where it is used: emails and online banking. Stronger encryption gives better data security.
Access Control
Access control answers one question: who is allowed in, and what may they do?
The most common access controls are usernames and passwords. Permissions go one step further: they limit what each user can do after logging in. For example, a user may read a file but not delete it. In this way, access control protects important resources and helps manage how the network is used.
Common Network Security Threats
The book names four common threats:
| Threat | What it does (book wording) |
|---|---|
| Viruses and malware | damage systems |
| Hackers | try to steal data |
| Phishing | tricks users to share information |
| Denial of Service attacks | stop network services |
Security tools, such as the firewalls, encryption and access control above, help reduce these threats.
Practice this topic
Short questions
1.What is network security?2 marks
Answer
From the book: "Network security is used to protect computer networks. It keeps data safe from unauthorized access. Security helps prevent data loss and damage." The chapter Summary defines it: "Network security refers to the methods used to protect networks, devices, and data from unauthorized access, misuse, or attacks."
2.Why is network security important?3 marks
Answer
From the book: "It is important for homes and organizations. Network security protects personal and important information. It stops hackers from entering the network. Security keeps data private and safe. It also protects devices from malware." Also: "Without security, networks become unsafe."
3.What is a firewall?2 marks
Answer
From the book: "A firewall is a security device or software. It controls incoming and outgoing network traffic. Firewalls block harmful or unwanted data. They act as a barrier between safe and unsafe networks."
4.What is encryption? Where is it used?3 marks
Answer
From the book: "Encryption changes data into a secret form. Only authorized users can read encrypted data. It protects data during transfer." Use: "Encryption is used in emails and online banking."
5.What is access control? Give its common examples.3 marks
Answer
From the book: "Access control decides who can use the network. It allows only authorized users to enter." Examples: "Usernames and passwords are common access controls. Permissions limit what users can do."
6.Name any four common network security threats.4 marks
Answer
From the book: "Viruses and malware damage systems. Hackers try to steal data. Phishing tricks users to share information. Denial of Service attacks stop network services." So the four threats are viruses and malware, hackers, phishing, and Denial of Service attacks. "Security tools help reduce these threats."
Long questions
1.What is network security? Explain firewalls, encryption and access control.8 marks
Answer
Cover the opening paragraph and the first three sub-headings of 1.14, using the book's text:
- Network security (verbatim): "Network security is used to protect computer networks. It keeps data safe from unauthorized access. Security helps prevent data loss and damage." "Network security uses different tools and rules." Summary definition: "Network security refers to the methods used to protect networks, devices, and data from unauthorized access, misuse, or attacks."
- Firewalls (verbatim): "A firewall is a security device or software. It controls incoming and outgoing network traffic. Firewalls block harmful or unwanted data (as shown in Figure 1.17). They act as a barrier between safe and unsafe networks. Firewalls protect computers from attacks. They are used in homes and offices." A labelled sketch of Figure 1.17: Firewall Protection earns marks.
- Encryption (verbatim): "Encryption changes data into a secret form. Only authorized users can read encrypted data. It protects data during transfer. Encryption is used in emails and online banking. Strong encryption improves data security. It prevents data theft."
- Access Control (verbatim): "Access control decides who can use the network. It allows only authorized users to enter. Usernames and passwords are common access controls. Permissions limit what users can do. Access control protects important resources. It helps manage network usage."
Aim for 250-350 words.
2.Explain the importance of network security. Describe the common network security threats.6 marks
Answer
Cover the opening paragraph and the sub-heading "Common Network Security Threats", using the book's text:
- Importance: "Many users connect to networks daily. Without security, networks become unsafe." "It is important for homes and organizations. Network security protects personal and important information. It stops hackers from entering the network. Security keeps data private and safe. It also protects devices from malware. Secure networks work smoothly without interruptions. Every network needs basic security measures."
- Threats (verbatim): "There are many threats to network security."
- "Viruses and malware damage systems."
- "Hackers try to steal data."
- "Phishing tricks users to share information."
- "Denial of Service attacks stop network services."
- Close: "Security tools help reduce these threats." Name the tools from the topic: firewalls, encryption and access control.
Aim for 200-300 words.
In this chapter
- 1.1Introduction to Computer Networks
- 1.2Network Architecture and Basic Concepts
- 1.3Types of Computer Networks
- 1.4Networking Devices
- 1.5Network Topologies
- 1.6Network Models and Layers
- 1.7Network Protocols and Services
- 1.8IP Addressing and Subnetting
- 1.9Home Network Setup and Configuration
- 1.10Wi-Fi Security and Router Configuration
- 1.11Network Diagnostic Tools and Commands
- 1.12Network Performance
- 1.13Network Load Balancing
- 1.14Network SecurityYou are here
- 1.15Data Backup and Recovery
- 1.16Usability and Security Tradeoffs