Denial of Service & Data Interception

Spec & Goals 3 min

AQA Spec 3.6.1.1 — Denial-of-service attacks; data interception and theft

By the end of this lesson you can:

1. Describe a denial-of-service (DoS) attack and its impact.
2. Explain data interception and theft (packet sniffing / man-in-the-middle).
3. State how each can be defended against.

Warm-Up 5 min

Some attacks don't steal anything — they just stop a service working. Others quietly copy data as it crosses a network. This lesson covers both.

Quick starter

If 100,000 fake customers all phoned a pizza shop at once, real customers couldn't get through. How is this like an attack on a website?

Key Concept — two very different attacks 14 min

Denial of service (DoS)

A denial-of-service attack floods a server or network with so many requests that it becomes overwhelmed and cannot respond to legitimate users.

When the flood comes from many hijacked computers at once (a botnet), it is a distributed denial-of-service (DDoS).

Data interception and theft

Data interception means capturing data as it travels across a network — for example using packet sniffing software, or a man-in-the-middle position on public Wi-Fi — and stealing the contents.

Worked Example — impact and defence 12 min

Problem: An online shop in Penang is hit on its busiest day: the site is flooded and goes offline; separately, customers on the shop's free Wi-Fi have card details stolen. Name each attack and defend it.

• Site flooded and offline → DoS/DDoS. Impact: customers can't buy → lost sales and reputation. Defence: firewall + traffic filtering to block the flood; rate-limit requests; scale up capacity.
• Card details stolen over Wi-Fi → data interception. Impact: theft of confidential data. Defence: encrypt the connection (HTTPS / secure Wi-Fi) so intercepted packets are unreadable.

Try It Yourself 12 min

📝 Exam Practice 10 min

Recap & Key Terms 3 min

A DoS attack floods a server so genuine users can't get in — it harms availability, not confidentiality. Data interception captures data crossing a network (e.g. packet sniffing) — defend it with encryption. DoS is defended with firewalls, filtering and capacity.

Denial-of-service (DoS)

Flooding a server with traffic so it cannot respond to legitimate users.

DDoS

A distributed DoS launched from many hijacked computers (a botnet) at once.

Data interception

Capturing data as it travels over a network in order to steal it.

Packet sniffing

Using software to capture and inspect packets travelling across a network.

Homework 1 min

Task (≤ 15 min): A bank suffers two incidents: its website is knocked offline for an hour, and a customer's data is stolen over public Wi-Fi. For each, name the attack, state one impact, and give one defence.