Email Security

    Botnets: Tools and Techniques for Detection, Prevention, and Removal

    Botnet detection is an important element of any organization’s cybersecurity program in order to prevent data theft, network disruption, reputational damage, and regulatory penalties.

    by Giulian Garruba

    Key Points

    • Botnets are networks of computers controlled remotely by a third party, used to carry out malicious cyberattacks such as sending spam messages and launching DDoS attacks.
    • Detection methods include network traffic analysis, signature-based detection, behavior-based detection, and machine learning algorithms. 
    • Prevention strategies involve keeping software up to date, using antivirus software, being cautious when opening emails or clicking on links, using firewalls with strong passwords, and more.

    As one of the most effective and flexible tools available to cybercriminals today, botnets are a constant threat to networks and devices, making proactive botnet detection an essential element of any organization’s cybersecurity program and a key component of security awareness and user behavior training. Ubiquitous and difficult to detect, botnets remain a concern for any organization regardless of the level of cybersecurity employed.

    In this article, we explore how botnets work, how to effectively detect botnets, how your cybersecurity team can remove botnets, and the main tools used in the detection and prevention of botnet attacks. Read on to learn more.

    What Is a Botnet?

    At its simplest, a botnet is a network of compromised computers (referred to as "bots") that are controlled remotely by a third party. These computers and other devices, or endpoints, typically link back to a command and control (C&C) server that distributes instructions to the bots. Once botnets gain a foothold within a device, they can quickly spread their influence across many more endpoints using either the Internet or closed networks, leveraging the processing power of each endpoint to build a network of bots that can be used to implement a range of malicious cyberattacks.

    Botnets can grow very quickly, and the most successful ones are very large and can operate under the radar for long periods of time. At these scales, they can inflict considerable damage over months and even years, relying on the difficulties involved in detecting them to spread and deploy a variety of cyberattacks that can be highly damaging to individuals and organizations.

    Today, complex botnets can be used to send spam messages, launch DDoS attacks, or steal sensitive information such as passwords and credit card numbers using keylogging systems. Thanks to their sheer size, they are also capable of conducting massive cyberattacks that can disrupt services and steal sensitive information.

    How Do Botnets Work?

    A botnet is created when an attacker gains unauthorized access to a computer and installs software that allows them to control the machine remotely. This software can spread from one compromised machine to others, creating a network of bots that can be used for malicious purposes. While each botnet is essentially unique, most will follow a variation of the following five steps:

    • Infection: The first step is to infect computers with malware, which typically spreads through phishing emails, infected software downloads, or vulnerabilities in operating systems and applications. The botnet itself is also capable of self-replication on some devices.
    • Command and Control (C&C): Once a computer is infected, it becomes part of the botnet and can receive commands from the botmaster (the person or entity controlling the botnet). The C&C server is used to issue commands and receive information from the bots in the botnet.
    • Task Assignment: The botmaster can use the C&C server to assign tasks to the bots in the botnet. These tasks can range from sending spam to conducting DDoS attacks.
    • Execution of Tasks: The bots in the botnet carry out the tasks assigned to them by the botmaster. They can perform these tasks simultaneously, making a botnet a powerful tool for the botmaster.
    • Reporting: The bots in the botnet typically report back to the C&C server, providing information about their status and the results of the tasks they have executed.

    Types of Botnets and Their Uses

    There are countless types of botnets currently in existence, with many displaying distinct architectures that make detecting botnets a challenge for cybersecurity professionals. Additionally, a botnet may be capable of multiple types of attacks once it has gained a foothold within a network, with command-and-control centers able to send instructions that fulfill a range of malicious purposes. Today, some of the most common uses of botnets include:


    In the same way that a single phishing email may attempt to trick a user into revealing sensitive information, such as login credentials or financial information, by posing as a trustworthy entity, a botnet phishing attack attempts to deploy phishing attacks at huge scales. This improves the odds of cybercriminals getting a “hit,” with only a small number of users required to click a malicious link or download malware for the attack to be considered a success.

    A phishing botnet operates by using compromised endpoints to send emails that contain a link that redirects the victim to a fake website that looks like a legitimate one. Alternatively, a user may unwittingly download malware from a link or attachment. Since the botnet usually has control of many endpoints, phishing emails can be sent at speed and in huge numbers from different sources with very little effort from the cybercriminal. This makes it more difficult for email filters and spam blockers to prevent messages from arriving in a user’s inbox.


    Similar to phishing botnets, and also capable of deploying phishing attacks, spambots are botnets that are used to send spam emails en masse. A spambot network leverages infected computers to send thousands of spam emails per minute, making it a lucrative tool for hackers who use it to spread malware, phish for personal information, or promote fraudulent products.

    One of the most common types of spambots is the Zeus Botnet, which has been used to steal sensitive information and spread malware. Other types of spambots include the Cutwail Botnet, which is primarily used to send out large quantities of spam, and the Grum Botnet, which was one of the largest spambots at its peak, sending millions of spam emails per day.

    Distributed Denial-of-Service (DDoS)

    Among the most common and concerning types of botnets are those that deploy Distributed Denial-of-Service (DDoS) attacks. Rising in frequency over the past decade, DDoS attacks target specific websites, using a large number of endpoints to flood a target network or website with traffic and render it unavailable to users. This disrupts the normal functioning of a website or network and causes significant financial and reputational damage to the target.

    DDoS botnets are created by infecting large numbers of computers with malware, allowing the attacker to control the infected machines remotely and use them in a coordinated attack. These botnets can range in size from a few hundred machines to hundreds of thousands of machines, and the size of the botnet directly affects the size and scale of the DDoS attack.

    There are several types of DDoS botnets, including: 

    • TCP Flood Botnets: These botnets send large amounts of traffic to the target using the Transmission Control Protocol (TCP) in an attempt to overwhelm the target's network and servers.
    • UDP Flood Botnets: These botnets use the User Datagram Protocol (UDP) to flood the target with traffic, causing the target's network and servers to become overwhelmed.
    • ICMP Flood Botnets: These botnets use the Internet Control Message Protocol (ICMP) to flood the target with traffic, causing the target's network and servers to become overwhelmed.
    • HTTP Flood Botnets: These botnets use the Hypertext Transfer Protocol (HTTP) to flood the target with traffic, causing the target's network and servers to become overwhelmed. 

    Why Is Botnet Detection Important?

    Since there is no universal model for what a botnet looks like or how it might act, comprehensive and progressive botnet detection is critical to your organization’s security. Additionally, as botnets can deploy varied types of cyberattacks in different ways, detection and subsequent botnet removal remain a priority for cybersecurity teams.     

    By detecting and stopping botnets, organizations can prevent DDoS attacks, spamming, and data theft, as well as protect networks, systems, and data. However, botnet detection is also important as they consume significant amounts of network and system resources, slowing down performance and making systems unavailable.

    Additionally, if your network is compromised, botnets may send spam and spread malware to partners, colleagues, clients, and customers. Removal of botnets which can damage an organization's reputation and credibility may help improve brand image and ensure your organization is trustworthy.

    Finally, certain regulations, such as the Payment Card Industry Data Security Standard (PCI-DSS), require organizations to implement measures to detect and prevent botnets. The detection and removal of botnets helps organizations to comply with these regulations and avoid penalties.

    Botnet Detection Methods

    Botnet detection remains a challenge for cybersecurity professionals around the world, with cybercriminals constantly evolving the technology to avoid detection. However, there are a number of botnet detection tools and techniques that can be used to detect botnets on networks and devices. Often, these are used in combination for more comprehensive coverage of the network and its users. Below, we look at each in more detail.

    How to detect botnets: 

    • Network Traffic Analysis: This type of botnet detection involves analyzing network traffic patterns to identify unusual or suspicious behavior that may indicate the presence of a botnet. This can include analyzing the volume, source, and destination of network traffic, as well as the types of packets being sent.
    • Signature-Based Detection: This method involves using known signatures or patterns of botnet activity to identify the presence of a botnet. This can include analyzing the behavior of specific types of malware, such as worms or Trojans, that are commonly associated with botnets.
    • Behavior-Based Detection: Analyzing the behavior of individual devices or systems on a network to identify bot-like activity is another type of botnet detection. This can include monitoring processes and file changes, as well as analyzing the types of network connections being made.
    • Honeypots: A honeypot is a decoy system that is designed to attract and detect botnets. By setting up a honeypot, organizations can observe the behavior of botnets and collect information about the methods and tools used in botnet attacks.
    • Machine-Learning-Based Detection: This botnet detection method uses machine learning algorithms to analyze network traffic and detect botnets. This can include analyzing patterns in network traffic, as well as the behavior of individual devices on the network. 

    Botnet Prevention Methods

    Since they can be difficult to detect, botnet prevention should always be your first goal:

    • Keep Software and Operating Systems Up to Date: Software vendors often release patches for vulnerabilities that botnets can exploit. Installing these updates as soon as they become available can help prevent your device from being infected.
    • Use Antivirus Software: Antivirus software can detect and remove malware that is used to create botnets. Make sure to keep the software up to date to ensure that it can detect the latest threats.
    • Be Cautious When Opening Email Attachments or Clicking on Links: Phishing emails are a common way for botnets to spread, and email security is key to botnet prevention. Be wary of emails that contain attachments or links from unknown sources, and only open them if you trust the sender.
    • Disable Unnecessary Services: If a service is not being used, it's best to disable it. Unused services can provide a vector for attackers to exploit and infect a device with malware.
    • Use a Firewall: A firewall can help prevent unauthorized access to your device, which can reduce the risk of infection.
    • Use Strong Passwords and Multi-Factor Authentication: Botnets often rely on brute-force attacks to gain access to devices. Using strong passwords and multi-factor authentication can make it more difficult for attackers to gain access.
    • Educate Users: As part of security awareness training and user behavior programs, educating users about the dangers of botnets and how to avoid becoming infected can be an effective way to prevent the spread of botnets.

    Botnet Removal Methods

    Once it has been detected, expedient botnet removal is crucial, as the longer it remains within a device or network, the more opportunities it has to spread amongst other devices. Due to the nature of botnets, there is no single method to remove them, and it is likely you will need to use a combination of the below tools and techniques to completely rid your systems of them. Additionally, it is important to remember that removing a botnet is only the first step, and the infected device may still be vulnerable to future infections.

    How to Remove a Botnet:

    • Disconnect from the Internet: Disconnecting the infected device from the Internet can prevent the botmaster from issuing further commands and receiving information from the bot.
    • Run an Antivirus Scan: Antivirus software can detect and remove the malware that is used to control the bot. It's important to use an up-to-date antivirus program, as older versions may not be able to detect newer strains of botnet malware.
    • Remove the Malware: Once the malware has been detected, follow the instructions provided by the antivirus software to remove it. This may involve restarting the device and entering safe mode to isolate and remove the malware.
    • Change Passwords: After removing the malware, it's important to change any passwords that may have been compromised. This can help prevent the botmaster from regaining control of the device.
    • Restore from a Backup: If the malware has caused significant damage to the device, restoring from a known-good backup may be the best option. This will erase all the data on the device and replace it with a known-good version.
    • Contact Law Enforcement: If sensitive information has been stolen or used in illegal activities, it may be necessary to contact law enforcement. They can help track down the individuals responsible and bring them to justice.
    • Educate Users: Educating users about the dangers of botnets and how to avoid becoming infected can be an effective way to prevent future infections.

    Botnet Defense and Protection with Mimecast

    As leaders in email security and resilience, Mimecast can help protect your organization from botnet infection and other email-based attacks using a range of best-in-class solutions tailored to your specific requirements. We offer organizations of any size a fast and easy integration with other security tools, advanced administration capabilities, and easy compliance with the latest regulations, as well as cutting edge AI solutions and fast incident response. This means our world-class email solutions can help prevent a comprehensive range of attacks, including botnet infection and phishing scams among many others.

    The Bottom Line

    While botnets continue to pose a threat to individuals and organizations around the world, it's critical that both professionals and consumers look for ways to prevent, detect, and remove them quickly and efficiently. Multi-layered approaches that include a variety of prevention and removal methods are often the most effective way to reduce the risk of infection, and user education remains a crucial tool within any organization to mitigate threats of all kinds.

    For more information on how Mimecast can help you detect and remove botnet attacks, contact us today and explore our blog for insights on the cybersecurity landscape.

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