What Are Botnets? Botnet Attacks Explained

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Botnets (derived from “robot networks”) are networks of computers or devices that have been compromised by malware and are under the control of a remote attacker (often called a botmaster or bot herder).

Bad actors can launch malicious attacks like distributed denial-of-service (DDoS), credential theft, service disruption, spam campaigns, or click fraud, or use botnets to gain unauthorized access to critical systems. Many of these could crash or cripple an organization’s IT infrastructure.

How do botnet attacks work?

A botnet attack is activated when a malicious actor takes control of multiple computers (zombie devices or bots) in a network and infects them with malware. These bots become a network of enslaved computers. The bot herder (or bot master) uses them to launch attacks on enterprise networks, such as sending spam, stealing sensitive data, or even crashing websites.

The bot herder uses a command-and-control (C&C) server to communicate with the zombie or bot computers—the infected computers that make up the botnet—and issue commands, allowing the attacker to coordinate the actions of the botnet and direct its resources toward a specific target.

Command-and-control servers in botnet attacks

There are two types of C&C servers: centralized and decentralized. Both are susceptible to botnet attacks, but the approach is different.

Centralized: Client-server model

On a centralized C&C server, the bot herder and bots are connected to the same central hub for communication and commands. The bot herder issues commands to the bots, and they respond by sending back information or executing the commands. 

This makes the C&C server a single point of failure, which can be taken down by law enforcement or security researchers.

Decentralized: Peer-to-peer (P2P) model

This model requires each infected device to communicate directly with other bots, and the bot herder can issue commands to the entire botnet or specific bots through a single bot. 

This type of C&C server has no single point of failure, making it more difficult for defenders to shut down.

Stages of building a botnet

There are three stages of building a botnet: prepare and expose, infect and grow, and activate.

Stage 1: Prepare and expose

In stage 1, the bot herder identifies internet-connected devices with exploitable vulnerabilities, such as computers, routers, servers, and Internet of Things (IoT) devices. The bot herder then scans for weaknesses in the targeted systems, which may include weak passwords, outdated software, or other security flaws, as a means to infiltrate the target system.

Stage 2: Infect and grow

In stage 2, the bad actor installs malware that turns the device into a zombie that can be controlled remotely. Malicious actors can infect enterprise digital assets in various ways, such as through social engineering techniques like phishing emails or exploiting software vulnerabilities.

The attacker then scans the infected device for more vulnerable devices and repeats the process, gradually building up a network of infected devices.

Stage 3: Activate

Finally, in stage 3, the bot herder activates the botnet by connecting it to a C&C server, allowing the attacker to control all infected systems remotely and use them for their intended malicious purpose, such as data harvesting, launching DDoS attacks, sending spam emails, or spreading malware.

3 types of botnets

Botnets come in three primary varieties: Internet Relay Chat (IRC), P2P, and spam.

Internet Relay Chat (IRC) botnets

Introduced in 1988, IRC is a protocol for text-based chat systems that’s used for instant messaging between internet-connected computers. An IRC botnet is a collection of machines infected with malware that can be controlled remotely via an IRC channel. IRC botnets are one of the oldest and most popular types of botnets and are easy to detect.

P2P botnets 

P2P botnets use a decentralized approach to communicate and propagate. In this case, the bot or zombie acts as a command distribution server and a client who receives commands. Compared to other types of botnets, this model is more resilient against defenses and difficult to shut down.

Spam botnets

Over 100 billion spam messages and emails are sent daily. Botnets transmit about 85% of these spam messages. The bot herder uses spam botnets to send out millions of unsolicited emails and malicious messages to propagate phishing campaigns that steal identities, or to distribute malware designed to compromise computers and other internet-connected devices.

7 Common Types of Botnet Attacks

Botnets can be used to execute a huge variety of malicious activity, but the most common are DDoS attacks, spam campaigns, banking trojans, credential stuffing, click fraud, crypto mining, and ransomware.

DDoS attacks

DDoS attacks overwhelm a target system or network with a flood of traffic from many sources in order to shut it down. Malicious actors use botnets to launch DDoS attacks because they can generate significant traffic from a large number of computers. 

There are different types of DDoS attacks, such as user datagram protocol (UDP) flood, TCP SYN (SYN means synchronization) flood, and HTTP flood, each of which uses a different method to generate traffic.

  • UDP flood attacks involve sending large numbers of UDP packets to a target system, overwhelming its ability to process incoming traffic. 
  • SYN flood attacks involve sending a large number of TCP SYN packets to a target system, which ties up its resources by forcing it to establish multiple half-open connections. 
  • HTTP flood attacks involve sending large numbers of HTTP requests to a target web server, overloading it with traffic.

Note: We reviewed the best DDoS protection services to thwart this kind of attack.

Spam campaigns

Attackers use botnets to send out large amounts of spam emails to spread malware and promote scams or phishing schemes. These emails can be difficult to filter or block because they come from many different sources.

Banking trojans

Bot herders can use botnets to deliver malicious software like banking trojans designed to steal sensitive information such as banking credentials, credit card details, and other sensitive financial and personal information. 

Banking trojans are often distributed through phishing emails or malicious websites. They’re difficult to detect because they operate and capture sensitive information in the background without the end user’s knowledge.

Credential stuffing

In this type of attack, the bot master fraudulently acquires large lists of credentials from data breaches or other sources. Then they attempt to use these stolen or guessed usernames and passwords on a target website or application, which may be another unrelated service, to gain access to user accounts. 

Credential stuffing attacks are often successful because many people use the same username and password across multiple websites. Using a different password for different services is recommended, and these passwords should contain a combination of uppercase and lowercase letters, numbers, and special characters. Password manager tools can help you easily manage your passwords and generate strong and different passwords for your numerous accounts.

Click fraud

Botnets can be used to generate fraudulent clicks on pay-per-click advertising campaigns, which can drain a company’s advertising budget. Click fraud can be difficult to detect because the clicks appear to come from legitimate sources, but in reality, they are generated by botnet-controlled computers.

Crypto mining

Botnets can use the computational power of the infected computers to mine cryptocurrency and generate revenue for hackers. Bitcoin mining requires significant computational power, and botnets can efficiently harness many computers’ resources to harvest currency without having to own the infrastructure themselves.


Attackers often use botnets to distribute ransomware through phishing emails or malicious websites in order to infect many computers at once. This malware encrypts a victim’s files and demands payment in exchange for the decryption key.

Common botnet targets and motives

A bot herder’s primary targets include but are not limited to computer systems, servers, networks, and websites. They target these devices in order to use them to execute malicious activities, such as DDoS attacks, spam campaigns, data theft, phishing, and click fraud.

Typically (though not always), a malicious actor’s main motive is to make money. They can monetize a botnet by selling access to it, generating income via click fraud, or using it to steal sensitive information to sell on the black market or deep web. Aside from the monetary incentives, attackers may also use a botnet to take down targeted critical systems or launch DDoS attacks for political or ideological reasons.

How to prevent botnet attacks

There’s no surefire way to prevent botnets, but you can considerably improve your defenses with the right strategy. To minimize risk, you’ll want to keep your software and devices up-to-date with patches, employ a capable firewall, keep on top of compliance and network traffic, and ensure that data is backed up regularly.

  • Update and patch software regularly: Ensure all enterprise software, including operating systems, web browsers, and plugins, are updated. Outdated software can contain vulnerabilities that can be exploited by botnets.
  • Use firewalls and antivirus software: When you run regular system scans, antivirus software can help detect and remove botnet malware from your devices, while firewalls can block intruders from gaining unauthorized system access.
  • Practice safe browsing habits: Avoid visiting websites you don’t trust, and don’t open suspicious emails or click on unfamiliar links.
  • Use strong passwords: It’s best to use strong and unique passwords for all accounts and change them regularly.
  • Monitor network traffic: By monitoring your network traffic regularly, you will have a better chance of detecting unusual activity, such as traffic spikes, unusual data transmission, and suspicious IP addresses.
  • Data backups: Regularly back up your important data to a secure offsite location that is not connected to your network. This can help you recover your data in case of a botnet attack or other data loss event.

Stopping and recovering from a botnet attack

Although stopping and recovering from a botnet attack is complex, minimizing the damage and preventing future attacks can be critical to protect your organization from disaster. Here are some steps you can take:

  1. Isolate infected devices: Rapidly disconnect any infected device from your enterprise network and the internet to prevent it from communicating with the C&C server.
  2. Scan and remove malware: Use reputable antivirus software to scan and remove any botnet malware from infected devices.
  3. Change passwords: Change all passwords for any accounts that may have been compromised.
  4. Block C&C communication: Use firewalls and other network security tools to block communication between infected devices and the C&C server. This will prevent the botnet from receiving commands or sending stolen data.
  5. Update software: Update all software and firmware on your devices, including operating systems, web browsers, plugins, and IoT devices. This can help prevent vulnerabilities that botnets can exploit.
  6. Monitor network traffic: Monitor your network traffic for unusual activity, such as outgoing data, connections to suspicious IP addresses, and unusual DNS queries.
  7. Restore from backups: This is where your disaster recovery plan comes in handy. After successfully removing the botnet malware, it’s time to begin healing. Initiate a data restoration plan by restoring data from backups. If available, follow the steps outlined in your company’s disaster recovery plan to complete this process.
  8. Seek professional help: Employ the services of a cybersecurity expert or a professional cybersecurity team to help fortify your system against future attacks. 

Bottom line: Protecting your organization from botnet attacks

Botnet attacks threaten enterprise security—and survival. Hence the need to take proactive steps to protect your enterprise systems against them. Experts recommend that companies invest in cybersecurity technologies to help them mitigate cyber attacks. Having a cybersecurity insurance policy can also help cover the cost of downtime and system restoration in the event of an attack.

We reviewed the best enterprise network security companies to help you keep your network secure and your sensitive data protected.

Aminu Abdullahi
Aminu Abdullahi
Aminu Abdullahi is an experienced B2B technology and finance writer and award-winning public speaker. He is the co-author of the e-book, The Ultimate Creativity Playbook, and has written for various publications, including eWEEK, Enterprise Networking Planet, Tech Republic, eSecurity Planet, CIO Insight, Enterprise Storage Forum, IT Business Edge, Webopedia, Software Pundit, and Geekflare.

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