The internet and its uses

People often mix up these two terms, but they are not the same.

• The internet 互联网 is the infrastructure 基础设施 — the huge worldwide network of computers and the cables, routers and connections that join them.
• The world wide web 万维网 (WWW) is a collection of websites 网站 and web pages that you view using the internet.

So the internet is the network; the web is one of the things you use on that network.

The internet is the worldwide network; the world wide web is one of the things you use on it

A router joins your home network to the internet and sends data to the right place

A uniform resource locator 统一资源定位符 (URL) is a text-based address for a web page. You type it into a web browser 网页浏览器 to visit a page, for example https://www.example.com/index.html.

A URL has three parts: the protocol, the domain name, and the path to the page on the server

A web browser is the program you use to view web pages. Its role includes:

• rendering 渲染 the hypertext markup language 超文本标记语言 (HTML) — turning the page's code into what you see;
• displaying web pages on the screen;
• managing how a web page is presented — its layout, text and images.

When you type a URL and press enter, several steps happen:

1. The browser needs the website's IP address 网际协议地址, but a URL uses a name, not a number.
2. The browser asks a domain name service 域名服务 (DNS) — a system that stores the IP address for each web address.
3. The DNS finds the matching IP address and sends it back to the browser.
4. The browser uses the IP address to contact the web server 网络服务器 that stores the page.
5. The web server sends the page's HTML back to the browser.
6. The browser turns the HTML into the page and displays it.

The browser asks a DNS for the site's IP address, then requests the page from the web server, which returns the HTML

If the DNS does not have the address, it asks another DNS server until the address is found.

A data centre full of servers: powerful computers that store websites and send them to you

Worked example. Break down the URL https://www.example.com/books/index.html. https is the protocol, the set of rules used to transfer the page (the s means the transfer is encrypted). www.example.com is the domain name, which identifies the web server and which a DNS server turns into an IP address. /books/index.html is the file path and file name of the resource stored on that server. Name each part together with its job: an answer that says "the first bit" and "the last bit" describes the URL without ever explaining it.

A cookie is a small text file that a website stores on your device. It lets the website remember things about you. There are two types.

A cookie is a small text file stored on your computer

Cookies are used to:

• save personal details so you do not type them again (such as login or address);
• track user preferences 用户偏好, such as your language or the things you like, so the site can suggest content.

A digital currency 数字货币 is money that exists only in electronic form 电子形式. There are no coins or notes. It is stored and moved between people using computers, and can be used to pay for things online.

A problem with digital money is trust: how do you stop someone spending the same money twice, or changing the records? Blockchain solves this.

A blockchain 区块链 is a digital ledger 数字账本 — a shared record of every transaction 交易. The record is copied across many computers, so no single person controls it and it is very hard to change.

The transactions are kept in blocks joined in a chain. Each block holds:

• the data of the transaction (who paid whom, and how much);
• a timestamp 时间戳 (the date and time);
• a hash value 哈希值 — a special code worked out from the block's contents.

Each block also stores the hash of the block before it. If someone changes an old block, its hash changes, so it no longer matches the next block. This breaks the chain and the change is spotted at once. This is how blockchain tracks transactions safely.

Each block stores the previous block's hash, chaining the blocks; changing one block breaks the chain

Cyber security 网络安全 means keeping computers, networks and data safe from attack. You must know these threats.

Types of malware

Malware is any software made to harm a computer. The main types are:

Impact of the threats

These attacks can steal personal data, delete or change files, stop a service from working, cost money, and make users lose trust in a company. For example, a DDoS attack can make an online shop unusable, so it loses sales.

You can protect data using these methods.

• access levels 访问权限 — each user can only see or change the data they need, nothing more.
• anti-malware 反恶意软件 software, including anti-virus 杀毒软件 and anti-spyware 反间谍软件 — scans for and removes harmful software.
• authentication 身份验证 — proving who you are before you get access. Methods include:
  • biometrics 生物识别 (fingerprint or face),
  • a password 密码,
  • two-step verification 两步验证 (a code sent to your phone as well as a password).
• automating software updates — updates fix weak points (bugs) in software automatically.
• checking the spelling and tone of messages — bad spelling or an odd, urgent tone can show a message is fake (phishing).
• checking the URL attached to a link — a wrong or strange web address warns you the link is unsafe.
• firewall 防火墙 — checks data going in and out of a network and blocks anything not allowed.
• privacy settings 隐私设置 — control who can see your information online.

A firewall sits between the outside internet and your network, checking each connection and blocking any traffic that is not allowed

• proxy server 代理服务器 — sits between the user and the internet, hiding the user's IP address and filtering out unsafe content.

• The internet is the worldwide network (the infrastructure); the world wide web is the pages you view on it — do not mix the two up.
• Learn how a page loads: the browser asks a DNS for the site's IP address, then requests the page from the web server, which returns the HTML.
• Match the malware types: virus (attaches to a file), worm (spreads by itself across a network), Trojan horse (pretends to be useful), spyware, ransomware.
• Match each threat to a defence: phishing/pharming → check the URL; brute force → strong passwords + two-step verification; interception → encryption; hacking/DDoS → a firewall.
• A session cookie is deleted when you close the browser; a persistent cookie is saved to remember you between visits.