The internet and its uses: IGCSE Computer Science Complete Notes

Ever Wondered What Actually Happens When You Open a Website?

Imagine you are standing in the middle of the world's busiest post office. Letters and parcels fly in every direction, sorted and routed automatically to the right destinations across the globe. That enormous postal system, connecting every office in every country, is a lot like the internet. And the websites you visit? They are more like the individual letters inside that system. Getting the difference between the postal network itself and the letters it carries is one of the first things Cambridge IGCSE Computer Science (0478) expects you to understand about this topic.

Let's break it all down, step by step, so you feel confident tackling any exam question on The Internet and Its Uses.

The Internet vs the World Wide Web

People use "the internet" and "the World Wide Web" as if they mean the same thing. They do not, and examiners love testing this distinction.

• The Internet is a global network of interconnected networks. It is the physical and logical infrastructure: undersea fibre-optic cables, routers, switches, and the protocols (like TCP/IP) that allow devices to communicate.
• The World Wide Web is a collection of web pages and resources, linked by hyperlinks, accessed through the internet using web browsers. Tim Berners-Lee invented it in 1989.

URLs: the Addresses of the Web

Every web page has its own address, called a Uniform Resource Locator (URL). Think of it as the full postal address for a letter. A URL has a clear structure:

protocol://domain-name/path

For example: https://www.example.com/notes/security

• Protocol - https tells the browser how to communicate with the server.
• Domain name - www.example.com is the human-friendly name for the server.
• Path - /notes/security points to a specific page or resource on that server.

HTTP vs HTTPS

How a Web Page Gets to Your Screen

Picture ordering food through a delivery app. You tap the restaurant name (the URL), the app finds the restaurant's actual street address (DNS lookup), sends your order (HTTP request), and the restaurant sends back your meal (HTML response). Your screen then arranges the food nicely on a plate (rendering).

Here is the technical version, step by step:

1. You type a URL into the browser's address bar (e.g. https://www.example.com).
2. The browser contacts a DNS server to resolve the domain name into an IP address (e.g. 93.184.216.34).
3. The browser sends an HTTP/HTTPS request to the web server at that IP address.
4. The web server processes the request and returns an HTML file (along with CSS and JavaScript).
5. The browser renders the HTML, applies CSS styling, and executes JavaScript to display the page.

Digital Currency

You have probably heard people talking about Bitcoin or cryptocurrency. But what exactly is a digital currency, and why does it appear on your IGCSE Computer Science syllabus?

What Is Cryptocurrency?

A cryptocurrency is a decentralised digital currency. There is no central bank or government controlling it. Instead, it relies on a network of computers working together to verify and record transactions.

How Blockchain Works

A blockchain is a distributed ledger: a record of all transactions shared across many computers (called nodes). Here is how it works in simple terms:

• Transactions are grouped into blocks.
• Each block contains a hash (a unique digital fingerprint) of the previous block, linking them in a chain.
• This chain structure means that altering one block would break every block after it, making tampering extremely difficult.
• Copies of the blockchain are stored across thousands of nodes worldwide, so there is no single point of failure.

How Transactions Are Verified

When you send cryptocurrency to someone, the transaction is broadcast to the network. Here is what happens next:

1. The sender uses their private key to digitally sign the transaction (proving they authorise it).
2. The network can verify the signature using the sender's public key (without revealing the private key).
3. Miners (or validators) compete to solve complex mathematical problems to verify the block of transactions.
4. Once verified, the block is added to the blockchain, and the transaction is confirmed.

Benefits and Risks of Cryptocurrency

Cyber Security

If the internet is the world's postal system, cyber security is the set of locks, alarms, and guards that stop criminals from stealing your letters or sending you fake ones. This is one of the most heavily examined parts of the internet topic in IGCSE Computer Science, so give it serious attention.

Cyber Threats

Threats come in many forms. Think of each one as a different type of criminal tactic:

Malware (Malicious Software)

Other Attack Methods

• Phishing - Fraudulent emails or messages that pretend to be from a trusted source (like your bank), tricking you into revealing personal information such as passwords or credit card numbers.
• Pharming - Redirects you from a genuine website to a fake one without your knowledge, usually by altering DNS records or infecting your computer. Even typing the correct URL leads to the fake site.
• Social engineering - Manipulating people (rather than systems) into giving away confidential information. A phone call pretending to be IT support asking for your password is a classic example.
• Brute force attack - Systematically trying every possible combination of characters until the correct password is found. Longer, more complex passwords take exponentially longer to crack.
• DDoS (Distributed Denial of Service) - Flooding a server with so many requests from multiple sources that it becomes overwhelmed and cannot serve legitimate users. Think of a thousand people trying to squeeze through one door at once.
• Data interception (Man-in-the-Middle) - An attacker secretly intercepts communication between two parties, reading or altering data in transit. Using unencrypted public Wi-Fi makes this much easier for attackers.

Cyber Security Prevention Methods

Knowing the threats is only half the battle. The exam will also test you on how to prevent them. Here are the key defences:

• Firewalls - Software or hardware that monitors incoming and outgoing network traffic, blocking suspicious connections based on security rules. Think of it as a bouncer at a club door checking who gets in and out.
• Encryption - Scrambling data so that only someone with the correct decryption key can read it. Even if data is intercepted, it appears as meaningless characters.
• Strong passwords - Use a mix of uppercase letters, lowercase letters, numbers, and special characters. Avoid dictionary words and personal information. A good minimum length is 8-12 characters.
• Two-factor authentication (2FA) - Requires two different forms of identification. For example, a password (something you know) plus a code sent to your phone (something you have). This means a stolen password alone is not enough to access the account.
• Biometrics - Using unique physical characteristics (fingerprint, face recognition, iris scan) for authentication. Extremely difficult to forge.
• Anti-malware software - Scans files and programs for known malware signatures, quarantining or deleting threats. Must be kept up to date to recognise new threats.
• Access levels and permissions - Giving users only the minimum level of access they need. A receptionist does not need the same system permissions as a database administrator.

Automatic Software Updates

Software updates are not just about new features. Many updates patch security vulnerabilities that attackers could exploit. Enabling automatic updates means your system receives these patches as soon as they are released, closing the window of opportunity for attackers. Delaying updates leaves known weaknesses exposed.

Worked Exam-Style Question

Model Answer:

Threat 1: Phishing
Attackers could send emails to employees pretending to be from a trusted source, tricking them into revealing login credentials.
Prevention: Train employees to recognise phishing emails - check the sender's address carefully, never click suspicious links, and report anything unusual. The company could also implement email filtering that flags known phishing patterns.

Threat 2: Ransomware
Malware could encrypt all customer data on the server, with attackers demanding payment for the decryption key.
Prevention: Keep regular backups of all data stored separately from the main server (offsite or in the cloud). If ransomware strikes, the company can restore from the backup rather than paying the ransom. Anti-malware software should also be installed and kept up to date.

Threat 3: DDoS Attack
Attackers could flood the company's server with traffic from many sources, making it unavailable to genuine customers.
Prevention: Use a firewall configured to detect and block unusual spikes in traffic. The company might also use a content delivery network (CDN) or DDoS mitigation service that absorbs and filters malicious traffic before it reaches the server.

Common Mistakes to Avoid

• Confusing the internet and the WWW. The internet is the infrastructure (hardware and protocols). The WWW is a service that runs on top of the internet. Always keep them separate in your answers.
• Forgetting DNS in the web page retrieval process. Many students jump straight from "user types URL" to "server sends page." You must mention that the DNS server resolves the domain name to an IP address.
• Mixing up viruses and worms. A virus needs user action to spread (opening a file). A worm replicates and spreads on its own across networks. Examiners test this distinction regularly.
• Saying "hacking" as a threat without being specific. "Hacking" is too vague for exam purposes. Name the specific attack type: brute force, phishing, DDoS, and so on.
• Confusing phishing and pharming. Phishing uses fake messages to lure you into giving up information. Pharming redirects your browser to a fake website even when you type the correct URL. The method of deception is different.
• Not matching prevention to threat. Training staff helps against social engineering, but it does not stop a DDoS attack. Always link your prevention method logically to the threat you are addressing.

Self-Check Questions

Test yourself before the exam. Try answering these without looking back at the notes above:

1. Explain the difference between the internet and the World Wide Web. (Hint: one is infrastructure, the other is a service running on it.)
2. Describe the steps involved in retrieving a web page after a user enters a URL into a browser. (Aim for at least four distinct steps.)
3. What is a blockchain, and why does it make cryptocurrency transactions difficult to tamper with? (Think about the chain of hashes and distributed copies.)
4. A worm and a virus are both types of malware. Explain one key difference between them.
5. A school wants to protect its network from unauthorised access. Suggest two security measures and explain how each one helps.

If you can answer all five confidently, you are in a strong position for this part of the IGCSE Computer Science exam. Keep revising, keep testing yourself, and remember: every question in the exam is just asking you to explain what you already know in a clear, structured way. You have got this.