A Denial-of-Service (DoS) attack is a cyber-attack aimed at making a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting the services of a host connected to the internet. DoS attacks typically function by overwhelming a targeted machine with redundant requests, rendering it unable to respond to legitimate traffic or causing it to slow down significantly.

How does it work?

The primary aim of a DoS attack is to overload the target system’s resources, so it cannot function correctly or access the network. This overload is typically accomplished by flooding the target system with unnecessary requests, forcing the system to slow down or, in severe cases, completely stop.

Several techniques are used to perform DoS attacks, including:

1. TCP/IP-based Attacks include SYN Flood, where an attacker initiates a connection with a server but does not complete it, causing the server’s resources to be tied up.

2. Teardrop Attack: An attacker sends fragmented packets and modifies the reassembly information. This results in the packets being unable to reassemble correctly, causing crashes or system hangs.

3. Smurf Attack: This involves the attacker sending many ICMP echo (ping) traffic to IP broadcast addresses, all having a spoofed source IP of the victim.

4. Ping of Death: The attacker sends multiple malicious pings to a server. Each of these pings is a packet more significant than the maximum allowable size, causing a buffer overflow.

Notable Historical DoS Attacks

1. Project Rivolta: In early 2000, a 15-year-old hacker, Mafiaboy, launched one of the most significant DoS attacks in history. He targeted high-profile websites, including CNN, eBay, Amazon, and Yahoo, which was the leading search engine at the time.

2. 2012 Spamhaus Attack: This attack targeted Spamhaus, a group that tracks spam and related cyber threats. Cyberbunker, a Dutch hosting firm, was accused of orchestrating a massive attack, peaking at a then-record 300 gigabits per second.

3. Dyn Attack (2016): Several websites, including Twitter, Reddit, and Netflix, were taken offline due to a massive DDoS attack on Dyn, a significant DNS provider. This attack was carried out using a botnet of Internet of Things (IoT) devices.

Detecting a DoS Attack

Detecting a DoS attack can be challenging due to the volumetric nature of these attacks. However, sure signs might indicate a DoS attack:

  • Prolonged network performance or inability to access a particular website
  • Disconnection of a wireless or wired internet connection
  • A massive amount of spam emails

If a system displays these symptoms, it might be experiencing a DoS attack. Network administrators usually use various tools to monitor network traffic to detect unusual or suspicious activities that may indicate a DoS attack.

DDoS vs. DoS: What is the main difference?

While both DoS and DDoS attacks aim to disrupt service, the main difference lies in their execution method. A DoS (Denial of Service) attack is performed by a single host targeting a service or server with the intent of overwhelming it.

On the other hand, a DDoS (Distributed Denial of Service) attack is a form of DoS attack where multiple compromised computers are used as a network of bots (called a botnet) to flood a server or network with traffic. Because of the various sources involved in the attack, a DDoS attack is usually more challenging to stop than a simple DoS attack.


DoS attacks, and their distributed version, DDoS, pose a significant threat to the internet. Understanding how these attacks work, how they can be detected, and their differences are crucial to mitigate their effects and effectively protect network resources. It’s essential to employ a robust security strategy that involves traffic monitoring and threat detection to respond promptly and adequately to these attacks.