Botnets are one of the most persistent threats in cybersecurity. By combining large numbers of compromised computers, servers and Internet of Things (IoT) devices into remotely controlled networks, attackers can generate significant computing power and traffic from distributed locations.
Botnets can be used for many malicious activities, including Distributed Denial of Service (DDoS) attacks, spam campaigns, credential theft, click fraud and cryptocurrency mining. Understanding what botnets are, how they operate and how they contribute to DDoS attacks is an important part of improving cyber resilience.
What Is a Botnet?
A botnet, short for "robot network", is a network of computers or devices that have been infected with malicious software and placed under the control of an attacker.
Each compromised device is commonly referred to as a bot. Once infected, the device may receive instructions remotely without the legitimate owner being aware that it has become part of a malicious network.
Botnets can include many different types of devices, such as:
- Personal computers
- Servers
- Smartphones
- Routers
- Cameras
- Internet of Things devices
- Other internet-connected systems
By controlling large numbers of distributed devices simultaneously, attackers can perform malicious activities at a scale that would be difficult to achieve from a single system.
The Anatomy of a Botnet
A traditional botnet generally consists of three primary components.
Botmaster
The botmaster, also known as the bot herder or botnet operator, controls the botnet and determines how the compromised devices will be used.
The operator may issue commands to launch attacks, distribute malware, collect stolen data or perform other malicious activities.
Bots
Bots are the compromised devices that form the botnet.
Once infected, these devices can remain connected to the network while waiting for instructions from the botnet operator. In many cases, the device owner may not notice any obvious signs that their system has been compromised.
Command and Control Infrastructure
Command and Control, commonly referred to as C&C or C2, enables communication between the botnet operator and compromised devices.
Through this infrastructure, attackers can distribute instructions, update malware, coordinate attacks and collect information from infected systems.
Botnets do not always rely on a single central server. Some modern botnets use distributed or peer-to-peer communication models to make their infrastructure more resilient against disruption.
How Do Botnets Work?
Botnets typically begin with the compromise of internet-connected devices.
Attackers may exploit software vulnerabilities, weak passwords, exposed services, malicious downloads or other security weaknesses to infect systems with malware.
Once compromised, the device connects to the botnet's control infrastructure and becomes available to receive commands.
As more devices are compromised, the botnet grows in size and can generate increasing amounts of traffic or computing power.
How Botnets Are Used in DDoS Attacks
One of the most common uses of botnets is launching Distributed Denial of Service attacks.
During a botnet-based DDoS attack, large numbers of compromised devices simultaneously send traffic, requests or connection attempts towards the same target.
Because attack traffic originates from many distributed IP addresses and geographic locations, distinguishing malicious traffic from legitimate users can become more difficult.
Large botnets may generate significant traffic volumes, request rates or connection loads, potentially overwhelming:
- Network bandwidth
- Firewalls
- Load balancers
- Web servers
- Applications
- APIs
- DNS infrastructure
- Other internet-facing services
Botnets can also use multiple DDoS attack vectors or change attack techniques during an incident in an attempt to bypass mitigation controls.
Other Common Uses of Botnets
Although DDoS attacks are a major use case, botnets can support many other forms of cybercrime.
Spam and Phishing Campaigns
Compromised devices can be used to distribute large volumes of spam emails, phishing messages, malicious links and malware.
Using many different devices and IP addresses can make these campaigns more difficult to block.
Data and Credential Theft
Some botnet malware is designed to collect sensitive information from infected devices, including login credentials, financial information and personal data.
Stolen information may then be used for fraud, account compromise or other malicious activities.
Click Fraud
Botnets can generate artificial interactions with online advertisements or websites.
This fraudulent activity can increase advertising costs, distort analytics and create false impressions of legitimate user engagement.
Cryptocurrency Mining
Attackers may use the processing resources of compromised devices to mine cryptocurrencies without the owner's knowledge.
When large numbers of systems participate, the combined computing power can become significant.
The Impact of Botnets
Botnets can affect individuals, organisations and critical online services in several ways.
Financial Loss
DDoS attacks, fraud, data theft and service disruption can create significant financial consequences for affected organisations.
Downtime may also result in lost transactions, reduced productivity and additional incident response costs.
Service Disruption
Botnet-driven DDoS attacks can affect the availability and performance of websites, applications and other online services.
If critical infrastructure becomes overwhelmed, legitimate users may experience slow responses, connection failures or complete service outages.
Data and Privacy Risks
Botnet malware may collect sensitive data from compromised devices, creating risks related to privacy breaches, fraud and identity theft.
Loss of Trust
Repeated security incidents and service outages can affect customer confidence and damage an organisation's reputation.
IoT Botnets and the Growing Attack Surface
The rapid adoption of IoT devices has expanded the number of systems that attackers may attempt to compromise.
Internet-connected cameras, routers, smart devices and other embedded systems may become attractive botnet targets when they use weak credentials, outdated software or exposed services.
Large numbers of poorly secured IoT devices can provide attackers with a widely distributed infrastructure for launching DDoS attacks.
Notable Botnets Used in DDoS Attacks
Several botnets have demonstrated how compromised devices can be used to generate large-scale attack traffic.
Mirai
Mirai became widely known for compromising Internet of Things devices and using them to launch significant DDoS attacks.
The malware targeted devices with weak or default credentials and demonstrated the potential scale of IoT-powered botnets.
BASHLITE
BASHLITE is another malware family associated with compromised Linux-based and IoT devices.
Infected systems can be controlled remotely and used to generate DDoS traffic or perform other malicious activities.
Reaper
Reaper targets vulnerable IoT devices by exploiting software vulnerabilities.
Rather than depending primarily on default credentials, it demonstrated how weaknesses in device software could also be used to expand botnet infrastructure.
How to Defend Against Botnets
Protecting systems from botnet activity requires a combination of endpoint, network and infrastructure security controls.
Keep Systems Updated
Operating systems, applications, firmware and security software should be regularly updated to reduce exposure to known vulnerabilities.
Strengthen Network Security
Firewalls, intrusion detection systems and intrusion prevention systems can help identify and block suspicious activity associated with compromised devices.
Secure Internet-Connected Devices
Default credentials should be changed, unnecessary services should be disabled and access to exposed devices should be restricted wherever possible.
Use Endpoint Protection
Antivirus, antimalware and endpoint detection technologies can help identify malicious software before a device becomes part of a botnet.
Monitor Network Traffic
Continuous monitoring can help organisations identify unusual traffic patterns, unexpected outbound connections and other indicators of botnet activity.
Prepare for Botnet-Driven DDoS Attacks
Because botnets are frequently used to generate distributed attack traffic, organisations should also evaluate whether their infrastructure and mitigation controls can withstand different DDoS attack scenarios.
Regular DDoS resilience testing can help identify weaknesses, evaluate mitigation performance and improve preparedness before a real-world attack occurs.
Building Resilience Against Botnet-Based Threats
Botnets continue to evolve as attackers adopt new techniques for compromising devices, maintaining command and control infrastructure and generating distributed attack traffic.
As the number of internet-connected devices continues to grow, organisations need to combine strong security controls, continuous monitoring, vulnerability management and DDoS resilience testing.
Understanding how botnets work and how they are used in DDoS attacks is an important step towards protecting internet-facing services and building a more resilient security posture.
