The Internet & Its Uses 🌐
What actually happens when you type a web address, what cookies know about you, how blockchain stops cheating — and every trick cybercriminals use, plus how to beat them.
🎯 What you'll unlock this chapter
- 🌐 The internet vs the World Wide Web, URLs, HTTP/HTTPS and browsers
- 🍪 How DNS finds a web page, and what session and persistent cookies do
- ⛓️ Digital currency, cryptocurrency and blockchain
- 🦠 Cyber threats: brute force, interception, DDoS, hacking, malware, phishing, pharming, social engineering
- 🛡️ Defences: access levels, anti-malware, authentication, biometrics, firewalls, proxy servers, SSL
- ✏️ All 6 coursebook activities and every worked example
🌐 Internet vs World Wide Web 5.1.1
🔗 URLs 5.1.2
A uniform resource locator is a text address for a website, typed into the browser's address bar:
protocol :// website address / path / file name
https :// www.example.co.uk / science / quiz.html
domain host . domain name . domain type . country code If the path is left out, you get the website's root (home) page.
🎮 URL Dissector
Type or paste any URL and see each part labelled.
🔒 HTTP and HTTPS 5.1.3
Hypertext transfer protocol is a set of rules for transferring files across the internet. When security such as SSL/TLS is used it becomes https (the "s" means secure) and you'll see a padlock in the address bar — data is encrypted between your browser and the server.
🧭 Web browsers 5.1.4
A browser lets you access and display web pages: it interprets HTML sent from websites and shows the text, images, video and sound. Most browsers have: a home page; bookmarks; a history; forward/back navigation; multiple tabs; cookies; hyperlinks (open in a new tab or the same one); a cache of stored data; support for JavaScript; and an address bar.
📖 Finding a web page with DNS 5.1.5
Every website is hosted on a web server with its own IP address. The domain name server (DNS) translates the URL into that IP address, so nobody has to memorise numbers. DNS servers hold a database (and cache) of URLs and IP addresses; more than one server may be involved:
- You type the URL; the browser asks DNS server 1 for the IP address.
- If server 1 can't find it in its database or cache, it asks DNS server 2.
- Server 2 finds it and sends the IP address back; server 1 stores it in its cache.
- The IP address is sent to your computer.
- Your computer contacts the web server, which sends the HTML files; the browser interprets the HTML and displays the page.
🎮 DNS lookup — with caching
Look up a site twice. The first time DNS server 1 has to ask server 2; the second time it answers straight from its cache.
- Pick a site and press Look up.
🍪 Cookies 5.1.6
Cookies are small files sent by a web server and stored by your browser — little look-up tables of (key, data) pairs such as (language, Thai) or (music, rock). Each visit, the site checks for its cookies to recall your preferences, track you, and customise the page.
Cookies let sites remember passwords and addresses, recognise you, keep your basket, track your habits and history, target adverts at you, store preferences and game progress, and switch language automatically.
🎮 The Cookie Jar
Shop on a pretend site and watch which cookies your browser stores. Then close the browser and come back.
💳 Digital currency 5.2.1
Digital currency exists only as data — no physical form, unlike fiat currency (notes and coins backed by governments). It's an accepted way to pay, can be transferred between accounts, and powers online and app banking (e.g. PayPal, Apple Pay). Traditional digital currency relies on a central bank, which raises confidentiality and security issues.
⛓️ Blockchain 5.2.2
A blockchain is a decentralised database: every computer in the network holds a copy of every transaction, with no central server, so nothing can be changed without the agreement of the network. Each new transaction creates a block containing:
- 📄 Data — sender, recipient, amount…
- 🔏 Hash value — a unique "fingerprint" made by an algorithm (usually SHA-256), including a timestamp
- ⬅️ Previous hash value — pointing back to the block before (the first, the genesis block, points to nothing)
Change any data and that block's hash changes, so the next block's "previous hash" no longer matches — the chain is broken and everything after it is invalid. To stop a hacker just rebuilding the chain quickly, each new block needs a proof-of-work (deliberately about ten minutes), checked by miners who earn commission. Uses: cryptocurrency exchanges, smart contracts, research, politics, education.
🎮 Break the blockchain
Each block's hash is a real SHA-256 of its data and the previous hash. Edit a transaction and watch the chain break. Then Mine blocks to repair it — proof-of-work means finding a nonce that makes the hash start with "00".
🔨 Brute force, interception, DDoS and hacking 5.3.1
Brute force attack
Systematically trying every combination until the password is found. Hackers start with the most common passwords (123456, password, qwerty…), then a word list of millions of words. Longer passwords with more types of character take far longer to crack.
Data interception
Stealing data by tapping into a wired or wireless link: a packet sniffer examines packets on a network; wardriving intercepts Wi-Fi from outside a building. Defences: encryption (e.g. WEP/WPA), firewalls, strong router passwords, and avoiding public Wi-Fi for anything private.
Denial of service (DoS / DDoS)
Flooding a server (or an email account) with useless traffic so it can't serve real users — no emails, websites or online banking. In a distributed attack the traffic comes from many computers, so it's hard to block. Defences: up-to-date malware checker, firewall, email filters. Signs: slow network, sites unavailable, lots of spam.
Hacking
Gaining illegal access to a system without permission — leading to identity theft and data deleted, changed or leaked. Encryption doesn't stop hacking (just makes stolen data meaningless). Defences: firewalls, user names, strong frequently-changed passwords, anti-hacking and intrusion-detection software. Ethical hacking is authorised, paid testing of a company's security.
🦠 Malware 5.3.1
| Type | What it does |
|---|---|
| Virus | Replicates itself to delete or corrupt files or make the computer malfunction. Needs an active host program (or an infected OS) and a trigger to run. Spread by email attachments, infected websites and software. |
| Worm | Stand-alone malware that self-replicates and spreads across networks through security holes — no host program or user action needed, so it's often more dangerous than a virus (e.g. the "I love you" worm). |
| Trojan horse | Malicious instructions disguised as legitimate software (e.g. a fake anti-virus "free trial"). The user runs it, so firewalls are bypassed. Often installs spyware or ransomware. |
| Spyware | Monitors your activity and sends data (passwords, card numbers) back to the criminal. Key logging software records key presses. Removed by anti-spyware. |
| Adware | Floods you with unwanted adverts (pop-ups, redirected searches); can expose security weaknesses and be hard to remove. |
| Ransomware | Encrypts your data and holds it hostage until a ransom is paid. Arrives via Trojans or social engineering. Best defence: regular back-ups. |
🎣 Phishing, pharming and social engineering 5.3.1
Social engineering manipulates people into breaking normal security procedures, exploiting fear, curiosity, and empathy and trust:
| Threat | How it works | Exploits |
|---|---|---|
| Instant messaging | Malicious links in messages, e.g. an "important upgrade" | Curiosity |
| Scareware | A pop-up claims you're infected; download the (fake) anti-virus now | Fear |
| Emails / phishing | A genuine-looking email links to a fake site | Trust |
| Baiting | An infected memory stick is left for someone to find and plug in | Curiosity |
| Phone calls | A fake "IT professional" gets you to install software giving them control | Fear / trust |
The stages of a scam: 1 identify the victim and plan; 2 target them (email, call, Trojan…); 3 execute the attack; 4 remove all traces.
🧑⚖️ Access levels and anti-malware 5.3.2
User accounts give different people different access levels (e.g. a hospital cleaner can't see patient records; a consultant can). Databases control who can read, write or delete, with different views of tables. Social networks offer levels like public, friends, custom and data owner, set with privacy settings.
Anti-spyware finds spyware by rules (typical spyware features) or file structures; it removes it, prevents downloads, encrypts files and key strokes, blocks webcam/microphone access and warns if your data has been stolen.
🔑 Authentication and passwords 5.3.2
Authentication proves who you are, using: something you know (password, PIN), something you have (a phone), or something unique to you (biometrics).
Strong passwords have at least one capital letter, one number and one other character (e.g. Sy12@#TT90kj=0); weak ones are easy to guess (GREEN, a pet's name, a birthday). Keep them safe: run anti-spyware, change them regularly, don't use personal information. Systems hide passwords as ••••, ask you to type new ones twice (verification), and lock you out after a few wrong tries (usually 3).
🎮 How long to crack it?
Type a made-up password (not a real one!) to check its strength and estimate how long a brute force attack would take at 10 billion guesses a second.
🧬 Biometrics 5.3.2
| Technique | ✅ Benefits | ⚠️ Drawbacks |
|---|---|---|
| Fingerprint (ridges and valleys, ~1 in 5000) | One of the most developed techniques; very easy to use; small storage needed | Seen as intrusive by some (linked with criminals); mistakes if the skin is dirty or damaged |
| Retina (infrared scan of blood vessels, ~1 in 10 million) | Very high accuracy; no known way to copy a retina | Intrusive; slow to verify; very expensive to install |
| Face recognition | Non-intrusive; relatively cheap | Affected by lighting, hair, age and glasses |
| Voice recognition | Non-intrusive; verification under 5 seconds; cheap | A voice can be recorded and replayed; illness such as a cold changes it |
Retina scan door: the scan goes through an ADC to a microprocessor, which compares it with stored scans; if they match, a signal (via a DAC and actuator) turns the light green and unlocks the door; otherwise it stays red and locked.
📲 Two-step verification and updates 5.3.2
Two-step verification uses two methods of authentication — e.g. a password (something you know) and then a one-time pass code sent to your registered phone (something you have). Automatic software updates install security patches and bug fixes (occasionally an update causes problems — you can roll back to a restore point).
🎮 Two-step verification
Log in to a pretend shop. Step 1: the practice username student and password Practice#1. Step 2: a one-time code is sent to "your phone".
✉️ Spotting scam emails 5.3.2
- 📧 Check the sender's address — the part after @ should match the company (not @gmail.com or random numbers).
- ✍️ Watch the tone and spelling — genuine companies don't rush you, or make grammar mistakes.
- 🔤 Look for misspelt domain names (typo squatting: amozon, gougle).
- 🔗 Hover over links — the destination should match the company; expect https for payments.
🎮 Spot the phish
This email has warning signs. Click on each one you find.
🧱 Firewalls, proxy servers, privacy settings and SSL 5.3.2
Firewall (software or hardware)
Sits between the computer and the external network and filters traffic both ways against set criteria, blocking and warning about anything that fails; logs traffic; blocks undesirable sites and IP addresses; helps stop viruses and hackers; warns when software tries to go online. It can't stop people bypassing it with their own devices, employee carelessness, or users who switch it off.
Proxy server
An intermediate between the user and a web server: filters traffic and can block sites; hides users' IP addresses; stops direct access to the web server, so attacks (hacking, DoS) hit the proxy instead; caches pages for faster access; can act as a firewall.
Privacy settings
Controls on browsers and websites limiting who can see your data: "do not track", saved-payment checks, safer browsing alerts (blacklists), history and cookie options, advertising opt-outs, and app permissions such as location sharing.
SSL (Secure Sockets Layer)
A protocol that encrypts data between the browser and web server (https + padlock):
- The browser asks to connect to the SSL-secured website…
- …and asks the web server to identify itself.
- The server sends a copy of its SSL certificate.
- If the browser can authenticate it, it tells the server to begin.
- The server acknowledges and encrypted two-way data transfer begins.
Used for online banking and shopping, email, cloud storage, intranets/extranets, VoIP, instant messaging and social networks.
✏️ Practice hub 6 activities · every example
Every activity from the coursebook chapter, as an auto-marked practice set with model answers for the written parts — fresh questions every time you hit 🔀 New questions.
📘 Worked examples
Every type of worked example in the chapter, solved step by step. Hit 🔀 Another example for a new one.
🃏 Key-term flashcards Tap to flip
🧠 Mini-quiz
📝 Exam-style questions Try, then peek
- ✅ The internet is the worldwide infrastructure of interconnected networks and devices (using TCP/IP).
- ✅ The WWW is the collection of web pages accessed over the internet using a browser and HTTP.
- ✅ The browser sends the URL to a DNS server.
- ✅ The DNS server finds the matching IP address (asking another DNS server if it isn’t in its database/cache) and returns it.
- ✅ The browser sends a request to the web server at that IP address.
- ✅ The server sends the HTML files; the browser interprets the HTML and displays the page.
- ✅ Each block stores the hash of the previous block; changing data changes that block’s hash.
- ✅ The next block’s previous-hash no longer matches, so the chain breaks and later blocks are invalid.
- ✅ Every computer holds a copy, and proof-of-work makes rebuilding the chain too slow to hide the change.
- ✅ Phishing uses fake emails that trick the user into clicking a link or giving personal details.
- ✅ Pharming uses malicious code (e.g. DNS cache poisoning) to redirect the browser to a fake site.
- ✅ Phishing needs the user to act; pharming happens without the user doing anything.
- ✅ Examines traffic between the computer and the internet against set criteria, blocking what fails and warning the user.
- ✅ Logs all incoming and outgoing traffic.
- ✅ Blocks undesirable websites/IP addresses; warns when software tries to access the internet.
- ✅ It sits between users and the web server, so there’s no direct access to the server.
- ✅ It hides users’ IP addresses and filters/blocks invalid traffic and certain IP addresses.
- ✅ Attacks such as DoS hit the proxy instead of the web server.
- ✅ It encrypts the user’s files and locks the computer until a ransom is paid — and paying doesn’t guarantee the key.
- ✅ Once run, the damage is almost impossible to reverse.
- ✅ Protect with regular back-ups, avoiding phishing emails/Trojans, and up-to-date anti-malware.
🚀 Going further A Level preview
TLS (Transport Layer Security) is the modern, more secure successor to SSL, providing encryption, authentication and data integrity. It has two layers: the record protocol (carries the data, encrypted or not) and the handshake protocol (the website and client authenticate each other and agree on encryption algorithms). TLS can also resume earlier sessions without repeating the whole handshake.