What is a Botnet?
At its core, a botnet is a group of compromised devices that a cybercriminal known as a botmaster or bot herder controls. In addition, the term combines “robot” and “network.” As a result, each infected device becomes a bot and can receive commands without its owner’s knowledge.
When someone asks, “What is a botnet?”, the direct answer is a remotely controlled network built from devices their owners did not knowingly contribute.
The simplest botnet meaning is a network of hijacked devices working together. Attackers use that combined computing power to send spam, steal credentials, spread malware, mine cryptocurrency, or overwhelm online services with traffic.
For example, one infected laptop can cause limited damage. However, thousands of infected devices acting at the same time can disrupt major services and make malicious traffic harder to distinguish from legitimate activity.
What is the Bot Definition in Cybersecurity?
The bot definition depends on context. A bot is any software program that performs automated tasks. Search engine crawlers, customer-service assistants, and monitoring tools are examples of legitimate bots.
In a botnet, however, a bot is a device or software agent that has been compromised and enrolled into an attacker-controlled network. It may also be called a zombie. The device can continue to function normally, so its owner may not realize it is being used for cybercrime.
How does a Botnet Work?
Typically, a botnet develops in four stages:
- Initial infection: Attackers exploit an unpatched vulnerability, use stolen or default credentials, or trick a user into opening a malicious link, attachment, or download.
- Malware installation: Malicious code gives the attacker persistent access and turns the device into a bot.
- Command and control: The infected device connects to command-and-control infrastructure, often called C2, to receive instructions.
- Coordinated activity: The botmaster commands many devices to act together against a target or perform tasks in the background.
For instance, some botnets rely on a central C2 server. In contrast, others use peer-to-peer communication, where bots pass commands among themselves. Therefore, security teams find peer-to-peer botnets harder to dismantle because no central server controls them.
What are Botnets Used for?
- Distributed denial-of-service attacks: Bots flood a website, application, or network with traffic until legitimate users cannot access it.
- Spam and phishing: Infected devices send large volumes of malicious email while concealing the attacker’s infrastructure.
- Credential and data theft: Bot malware may capture passwords, financial information, browser data, or sensitive files.
- Malware delivery: Attackers can use an established botnet to install ransomware, spyware, or other payloads.
- Cryptojacking: Bots use the victim’s processing power and electricity to mine cryptocurrency.
- Click and ad fraud: Automated traffic creates fake views or clicks to generate fraudulent advertising revenue.
- Proxy services: Criminals route malicious traffic through compromised devices to hide its source.
Which Devices can Become Part of a Botnet?
In practice, any internet-connected device with exploitable software, weak credentials, or poor security controls can become a bot. Common targets include:
- Employee laptops and desktop computers;
- Web and cloud servers;
- Smartphones and tablets;
- Routers and network appliances;
- Security cameras and digital video recorders;
- Printers, smart TVs, and other IoT devices; and
- Operational technology connected to enterprise networks.
For example, attackers frequently target IoT devices because many remain exposed to the internet, use default passwords, or receive software updates inconsistently.
What are the Signs of a Botnet Infection?
Nevertheless, a single symptom does not confirm an infection. However, security teams should investigate devices showing several of these behaviors:
- Unexplained network traffic or repeated connections to unfamiliar domains and IP addresses;
- Sudden performance degradation, overheating, or high CPU usage;
- Unauthorized changes to system settings or security controls;
- Unexpected outbound email or messaging activity;
- New processes, scheduled tasks, or startup items;
- Repeated login attempts against other systems; and
- Unusual DNS requests or regular outbound beaconing.
Additionally, modern bot malware often tries to stay quiet. As a result, network and endpoint telemetry may reveal an infection before a user notices any change.
How can Organizations Detect and Stop Botnets?
- Patch internet-facing systems: Fix known vulnerabilities in operating systems, applications, routers, and IoT devices.
- Remove default credentials: Use unique passwords and multi-factor authentication wherever the device supports it.
- Monitor endpoints and network traffic: EDR and NDR tools can identify malicious processes, command-and-control traffic, and unusual device behavior.
- Use threat intelligence: Known malicious domains, IP addresses, file hashes, and attacker behavior can improve detection. Learn more about threat intelligence.
- Segment networks: Isolate IoT, guest, and operational devices to restrict lateral movement and reduce the reach of a compromised system.
- Filter malicious traffic: DNS security, email controls, firewalls, and web filtering can block common infection and command channels.
- Contain infected devices: Disconnect compromised systems, preserve evidence, remove the malware, rotate exposed credentials, and investigate related activity through a formal incident response process.
Botnet vs. Malware: What is the Difference?
For example, malware is malicious software designed to disrupt, damage, spy on, or gain unauthorized access to a system. By contrast, a botnet forms when malware or another compromise places many devices under common control.
In short, malware may create the infection. Consequently, the botnet turns many infected devices into shared attack infrastructure.
Why do Botnets Matter to Enterprises?
On the one hand, an enterprise can be a botnet target, a source of botnet traffic, or both. For example, a botnet may disrupt customer-facing services through a DDoS attack. Meanwhile, an infected corporate device can expose credentials, consume resources, spread malware, and create legal or reputational risk.
Effective defense requires visibility across endpoints, networks, cloud systems, and identity activity. A Security Operations Center can correlate those signals, investigate suspicious behavior, and contain compromised devices before attackers use them at scale.
