O Level Computer Science: The Internet and Its Uses — Revision Notes

Topic 5 of Cambridge O Level Computer Science (2210) is mostly about sequences and pairs: the steps from URL to displayed page, the steps of an SSL connection, session versus persistent cookies, phishing versus pharming, and each cyber threat matched with its defence. These notes set each one out in the shortest form that still earns full marks on Paper 1.

Condensed for the final weeks. For the full explanation, use the Internet and its uses study guide; to apply it, use the Internet and its uses practice questions.

Syllabus coverage (2210, 2026–2028)

Ref	What you must be able to do
5.1.1	Tell the internet (infrastructure) from the world wide web (websites and pages)
5.1.2	Understand a URL: protocol, domain name, web page/file name
5.1.3	Describe the purpose and operation of HTTP and HTTPS
5.1.4	Explain the purpose and functions of a web browser
5.1.5	Describe how a page is located, retrieved and displayed
5.1.6	Explain session and persistent cookies and their uses
5.2.1–5.2.2	Digital currency and blockchain
5.3.1	Processes and aims of cyber security threats
5.3.2	Solutions that keep data safe

Five sequences to be able to write

A. URL to page: URL typed → domain name sent to DNS → DNS finds IP address (asks another DNS if needed) → IP address returned to browser → browser requests page from web server → server sends HTML → browser renders it.

B. SSL connection: browser asks server to identify itself → server sends its digital certificate → browser checks the certificate is valid → encrypted session agreed → data encrypted both ways.

C. DDoS attack: computers infected with malware form a botnet → attacker commands them to send requests to one server → server is overloaded → genuine users cannot get through.

D. Brute-force attack: software tries combinations of characters (often common passwords first) → continues until the password is found → attacker logs in.

E. Blockchain record: a transaction is made → it is time-stamped and added as a block → the block is linked to the previous block → copies are held across many computers → altering a block breaks the chain and does not match other copies.

Pairs that are easy to confuse

Pair	First	Second
Internet vs WWW	The network infrastructure	Websites and pages accessed over it
HTTP vs HTTPS	Rules for transferring pages	Same rules, data encrypted
Session vs persistent cookie	Deleted when the browser closes	Kept until expiry or deletion
Phishing vs pharming	User clicks a link in a fake message	User is redirected to a fake site even when typing the correct URL
Virus vs worm	Needs an infected file to be run	Replicates across a network on its own
Spyware vs adware	Secretly records user activity	Displays unwanted adverts
Firewall vs proxy server	Filters traffic by rules	Sits between user and internet, hides the user’s IP address and can filter

Threat → best defence

Threat	Defence to name
Brute-force attack	Authentication: a strong password, biometrics or two-step verification
Data interception	Encryption — HTTPS / SSL
DDoS attack	Firewall or proxy server filtering the traffic
Hacking	Firewall, strong authentication, access levels
Malware	Anti-malware software, automating software updates
Phishing	Checking spelling and tone, checking the URL attached to a link
Pharming	Checking the URL and the site’s certificate (SSL), anti-malware
Social engineering	Checking the spelling and tone of communications; access levels to limit what a tricked user can reveal

Cookie uses (from the syllabus)

Saving personal details · tracking user preferences · holding items in an online shopping cart · storing login details.

2210 and its sibling syllabus

The subject content of 2210 is shared with Cambridge IGCSE Computer Science (0478). If you use an 0478 textbook, its Topic 5 chapters match this syllabus exactly.

Exam traps

Drawn from our practice page, which paraphrases the Cambridge 2210 June 2025 mark schemes and lists where marks are usually lost:

• In the URL-to-page diagram, each step had its own mark, including the IP address being returned before the web server is contacted. Do not skip steps.
• The SSL marks were for the certificate being requested, sent and checked, not just “SSL encrypts the data”.
• Cookie answers need how long each type is kept, not just what it is for.
• Keep the roles separate: the browser renders, the DNS looks up the IP address, the web server stores and sends the page.

Frequently asked questions

What are the three parts of a URL in 2210? The protocol (such as https), the domain name and the web page or file name. Questions often give a URL and ask you to label each part.

Is ransomware a type of malware? Yes. The 2210 syllabus lists six types of malware: virus, worm, Trojan horse, spyware, adware and ransomware.

What does a proxy server do for security? It sits between users and the internet, so the user’s IP address is hidden from websites, and it can filter traffic and block access to unsafe sites.

Self-test

1. Name the component that turns a domain name into an IP address.
2. State two functions of a web browser besides rendering HTML.
3. Which cookie type holds items in a shopping cart during one visit?
4. Describe how a worm differs from a virus.
5. Give two ways a user could spot a phishing email.

Answers: 1. The domain name server (DNS). 2. Any two: storing bookmarks/favourites, recording history, multiple tabs, storing cookies, navigation tools, address bar. 3. A session cookie. 4. A worm replicates and spreads across a network by itself; a virus needs an infected file to be run. 5. Poor spelling or an urgent, threatening tone; a link whose URL does not match the genuine organisation.