The internet and its uses

Worth about 11 of the 75 marks on a typical Paper 1. Cyber security threats and how a web page is located come up most.

1. The internet and the world wide web

The internet is the infrastructure: the worldwide network of connected computers, cables and routers. The world wide web is the collection of websites and web pages that are accessed using the internet. Email and online games use the internet too, but they are not the web.

2. URLs

A uniform resource locator (URL) is a text-based address for a web page.

Part	Example	Meaning
Protocol	https	The rules used to transfer the page
Domain name	www.revisionhub.online	The name of the web server
Web page / file name	/igcse/hardware.html	The page or file on that server

3. HTTP and HTTPS

Hypertext transfer protocol (HTTP) is the set of rules for transferring web pages between a web browser and a web server.

HTTPS is the secure version. It uses the SSL/TLS protocol to encrypt the data sent between the browser and the server, and a digital certificate to prove the server is genuine. Browsers show a padlock. Use HTTPS whenever personal or payment details are sent.

4. Web browsers

The main purpose of a web browser is to render HTML and display web pages. Its other functions include:

• storing bookmarks and favourites
• recording the user’s history
• allowing multiple tabs
• storing cookies
• providing navigation tools (back, forward, refresh)
• providing an address bar

5. How a web page is found and displayed

1. The user enters a URL into the browser.
2. The browser sends the domain name to a domain name server (DNS).
3. The DNS finds the matching IP address (or asks another DNS) and sends it back to the browser.
4. The browser sends a request to the web server at that IP address.
5. The web server sends the page’s HTML to the browser.
6. The browser renders the HTML and displays the page.

6. Cookies

A cookie is a small text file that a website stores on the user’s computer. Cookies are used for saving personal details, tracking user preferences, holding items in an online shopping basket and storing login details.

	Session cookie	Persistent cookie
How long it lasts	Deleted when the browser is closed	Stays on the device until its expiry date or until the user deletes it
Where it is kept	Temporary memory	Secondary storage
Example	Items in a shopping basket during one visit	Remembering login details or language settings for next time

7. Digital currency and blockchain

A digital currency only exists electronically, such as Bitcoin. It is used to pay for goods and services online, without a physical coin or note.

Blockchain is a digital ledger: a time-stamped series of records that cannot be altered. Each block holds transaction details, a time stamp, its own hash and the hash of the previous block. Copies of the chain are held on many computers. If anyone changes a block, its hash changes and the chain no longer matches, so tampering is obvious.

8. Cyber security threats

Threat	What happens	Aim
Brute-force attack	Software tries every possible password combination until one works	Gain access to an account
Data interception	Data is captured while it travels across a network, e.g. by packet sniffing	Steal data in transit
DDoS attack	Many infected computers (a botnet) flood a server with requests until it cannot respond	Stop a website or service working
Hacking	Gaining unauthorised access to a computer system	Steal, change or delete data
Virus	Attaches to a file and replicates when the file is run	Damage or delete data
Worm	Replicates itself across a network without the user doing anything	Spread and use up resources
Trojan horse	Malware disguised as legitimate software	Install other malware or give remote access
Spyware	Secretly records activity, such as key presses, and sends it to a third party	Steal passwords and personal data
Adware	Displays unwanted adverts	Make money from adverts
Ransomware	Encrypts the user’s data and demands payment to unlock it	Extort money
Phishing	A fake email or message with a link to a fake website	Trick the user into giving personal details
Pharming	Malicious code redirects the user to a fake website, even when they type the correct URL	Steal personal details
Social engineering	Manipulating people into revealing information or breaking security rules	Gain access or information

9. Keeping data safe

Solution	How it helps
Access levels	Users can only see or change the data they need
Anti-malware (anti-virus, anti-spyware)	Scans files, quarantines and removes malware
Authentication	Usernames and passwords, biometrics (fingerprint, face) and two-step verification prove who the user is
Automatic software updates	Fix security weaknesses as soon as patches are released
Checking spelling and tone	Poor spelling or urgent, threatening tone can reveal a phishing message
Checking the URL of a link	Spots links that lead to fake websites
Firewall	Monitors traffic coming in and out and blocks anything that breaks its rules
Privacy settings	Control who can see your personal information
Proxy server	Sits between the user and the internet; hides the user’s IP address and can filter traffic
SSL	Encrypts data sent between the browser and the web server

10. Examiner tips

1. The internet ≠ the web. The internet is the infrastructure; the web is the pages accessed over it.
2. Describe how a threat works, not just its name, and say what the attacker wants.
3. Virus vs worm: a virus needs a file to be run; a worm spreads by itself.
4. Phishing vs pharming: phishing uses a fake email with a link; pharming redirects you even when you type the right URL.
5. Encryption doesn’t stop interception; it makes intercepted data meaningless.
6. A firewall doesn’t protect data in transit. Match the solution to the threat.
7. In the URL steps, name the DNS, IP address, web server and HTML in order.
8. Session vs persistent: the difference is how long the cookie lasts.

11. Practice questions

12. Topic test: predict your grade