A botnet is a network of infected devices controlled by a bot herder to carry out botnet attacks. Botnets are used for DDoS attacks, spam campaigns, credential theft, and distributing malware to new targets.

Botnet Explained: How Botnet Attacks Work and How to Stop Them

Q: Are IoT devices at risk of botnet infections?

Yes. IoT devices like routers, cameras, and smart TVs are among the most common targets for botnet infections because they often ship with weak default passwords and rarely receive updates.

What Does the Term Botnet Mean?

A botnet is a network of computers and devices that have been taken over by malware and are under the control of a single attacker. The term botnet comes from the words “robot” and “network.” Each device in a botnet is called a bot, and the person who runs it is called a bot herder. Once a device is part of a botnet, it follows orders from the bot herder without the owner knowing.

Scale of the Botnet Threat

Botnets are not new, but they are growing fast. In short, they are one of the most common and dangerous threats in cybersecurity today. DDoS attacks powered by botnets surged 121% in a single year, reaching over 47 million incidents (Cloudflare). The largest recorded botnet attack hit 31.4 terabits per second, a scale that was hard to imagine just a few years ago.

So how do botnets work? How do infected devices end up under the control of a stranger? And what can you do to stop your systems from becoming part of a botnet? This guide covers everything from how botnet infections happen to how you can defend against botnet attacks. Whether you run a small business or manage enterprise infrastructure, the risks are the same. Any device with an internet connection can become part of a botnet. Understanding the threat is the first step toward building a strong defense that keeps your systems clean and your data safe from harm.

Botnet at a Glance

A botnet is a group of infected devices controlled by a bot herder to carry out types of attacks such as distributed denial of service ddos attacks, credential theft, spam campaigns, and brute force login attempts. Botnets can include PCs, servers, routers, cameras, and internet of things iot devices. The bot herder issues commands through a command-and-control (C2) server or a peer to peer network.

How Botnets Work

Understanding how botnets work is the first step toward stopping them. A botnet follows a clear life cycle: infect, connect, and attack. Each stage builds on the last, and the whole process can happen in minutes. Millions of devices are pulled into these networks every year, most of them without the owner ever knowing. The alarming speed at which modern malware spreads means that a new threat can infect thousands of devices before anyone notices.

Stage 1: Infection

First, the bot herder spreads botnet malware to as many devices as possible. This malware can arrive through phishing emails, drive-by downloads, or by exploiting known software flaws. Internet of things iot devices like routers, cameras, and smart TVs are prime targets because they often run with default passwords and rarely get updates. Once the malware lands on a device, it installs itself quietly and turns the device into a bot.

Botnet infections also spread through brute force attacks on weak login credentials. Attackers use lists of common passwords to break into devices that face the internet. Consequently, any device with a weak password can become part of a botnet in seconds. This is why strong passwords and regular updates are your first line of defense. Weak credentials and unpatched software are the two biggest gifts you can give to an attacker looking to grow their army of bots.

Stage 2: Command and Control

After infection, the bot connects back to the bot herder’s command-and-control (C2) server. This server issues commands to all the infected devices in the botnet at once. The bot herder can tell the bots to attack a target, send spam, steal sensitive information, or download more malware. There are two main models for this setup.

In the client-server model, all bots report to a single C2 server. This is simple to run but also simple to shut down. If law enforcement finds and takes down the server, the botnet loses its brain. In the peer to peer model, bots talk to each other directly. There is no single point of failure, which makes these botnets much harder to disrupt. Modern botnets often use peer to peer networks or even blockchain-based channels to stay alive longer. Some recent botnets have used smart contracts on public blockchains to store C2 instructions, making takedowns nearly impossible through traditional methods.

Stage 3: Attack

Once the botnet is ready, the bot herder launches the attack. The type of attack depends on the goal. Some botnets control millions of infected devices and can launch distributed denial of service ddos attacks that overwhelm even the largest targets. Others quietly steal sensitive information, harvest credentials, or send spam to millions of inboxes. The massive scale of these attacks is what makes them so dangerous. A single attacker can control millions of infected machines and direct them all at once. The sheer scale is what makes botnet attacks different from other threats. One person with a botnet can do more damage than a large team of skilled hackers working on their own with manual tools.

Practitioner Tip

Monitor outbound network traffic from your devices. Bots phone home to their C2 servers on a regular schedule. Unusual spikes in outgoing traffic, especially to unknown IP addresses, are a strong sign that a device may be part of a botnet. Early detection can stop botnet infections before they cause damage.

Types of Botnet Attacks

Botnets are tools, and attackers use them for many different types of attacks. Each type exploits the scale and stealth that a botnet provides. Here are the most common botnet attacks you need to know about.

DDoS Attacks

Distributed denial of service ddos attacks are the most well-known use of botnets. The bot herder directs all infected devices to flood a target with network traffic at the same time. This overwhelms the target’s servers and knocks them offline. The largest botnet-driven DDoS attack on record hit 31.4 Tbps (Cloudflare).

Credential Stuffing and Brute Force

Botnets use stolen username and password lists to try logging into thousands of accounts at once. Each bot tries a small number of attempts, so the attack looks like normal traffic. Brute force attacks use the same method but try every possible password. Both types of attacks can crack weak credentials in minutes.

Spam and Phishing Campaigns

Botnets send spam emails at massive scale. A single botnet can send spam to millions of addresses per day. These emails often carry botnet malware or phishing links designed to steal sensitive information. Because each email comes from a different infected device, spam filters have a hard time blocking them all.

Data Theft and Espionage

Some botnets are built to steal sensitive information quietly. They log keystrokes, capture screenshots, or scrape files from infected machines. The stolen data is sent back to the bot herder through the C2 channel. This type of botnet attack can go undetected for months because the bots stay silent between data pickups.

Other Botnet Attack Types

Beyond these main types of attacks, botnets also mine cryptocurrency on infected devices, serve as proxy networks for hiding criminal traffic, and deliver ransomware payloads. Some botnets even sell access to their infected machines as a service, letting other criminals rent them for their own botnet attacks. This “botnet-as-a-service” model has lowered the cost of launching large-scale attacks. For more on how malware spreads and evolves, see our deep dive.

The Business Impact of Botnet Attacks

Botnet attacks do not just cause technical problems. They hit the bottom line hard. When a DDoS attack takes a website or service offline, the company loses revenue for every minute of downtime. Customer trust drops. Regulatory fines pile up if the attack exposes customer data. The costs add up fast, especially for small and mid-size businesses that may not have the resources to recover quickly.

Direct Costs of a Botnet-Driven Breach

When infected devices in a botnet steal sensitive information, the fallout includes breach notification costs, legal fees, and credit monitoring for affected customers. Companies may also face fines under data protection laws like GDPR or HIPAA. The average cost of a data breach continues to rise each year. According to IBM, the global average now exceeds $4 million. Many of these breaches start with a device that became part of a botnet without the owner knowing. The initial access that the bot provides is often the most expensive link in the chain, because it opens the door to everything else.

Additionally, organizations hit by distributed denial of service ddos attacks often need to invest in mitigation tools and extra bandwidth. These costs are not one-time expenses. Once you become a target, repeat attacks are common. Some attackers even demand ransom in exchange for stopping a DDoS flood. This practice, known as ransom DDoS, has become a steady revenue stream for bot herders who control large botnets.

Reputation and Customer Trust

Beyond direct costs, there is the damage to reputation. Customers who cannot reach your website during a DDoS attack may switch to a competitor. Partners may question your security posture. If a breach exposes that your devices were infected machines used in attacks against others, the reputational harm is even worse. You become both a victim and an unwitting participant in someone else’s crime. Proactive defense against botnet infections is therefore not just a technical concern. It is a core business priority for any organization that relies on its online presence.

Architecture Models: Client-Server vs Peer to Peer

How a botnet is built shapes how hard it is to take down. There are two main designs, and knowing the difference helps defenders plan their response.

Feature	Client-Server Botnet	Peer to Peer Botnet
Control method	Central C2 server issues commands	Bots relay commands to each other
Single point of failure	✓ Yes, C2 server	✕ No single point
Takedown difficulty	✓ Easier for law enforcement	✕ Much harder to disrupt
Stealth	◐ Moderate	✓ High
Modern use	Still common for simple botnets	Preferred by advanced botnets

In a client-server botnet, the bot herder runs one or more C2 servers that issue commands to all infected devices. This model is straightforward to build and manage. However, if law enforcement or security teams find and shut down the C2 server, the entire botnet goes dark. Consequently, many bot herders have moved to decentralized designs.

In a peer to peer botnet, there is no central server. Instead, each bot acts as both a client and a server, passing commands along to other bots. This makes the botnet far more resilient. Even if several bots are taken offline, the rest keep working. Some modern botnets even use encrypted blockchain channels for their C2 traffic, which makes them almost impossible to intercept through normal network traffic analysis.

Why Botnets Are Growing: IoT and the Attack Surface

The rapid growth of internet of things iot devices has been a gift to botnet operators. Routers, security cameras, smart TVs, baby monitors, and even kitchen appliances are now connected to the internet. Many of these devices ship with default passwords, run outdated firmware, and lack basic security controls. As a result, they are easy targets for botnet infections.

The Aisuru botnet, one of the largest ever recorded, grew by compromising millions of routers and cameras from brands like Totolink, Zyxel, and D-Link. In one case, the bot herder breached a router maker’s firmware update server. This single intrusion let the botnet grow past 100,000 infected devices overnight. When internet of things iot devices are this easy to compromise, the botnets control grows fast.

47M

DDoS attacks in a single year (Cloudflare)

31.4Tbps

Largest recorded botnet DDoS attack

3M+

Devices in the Aisuru/Kimwolf botnet

Moreover, cheap off-brand devices sold globally often come with disabled security features or even pre-installed malware. These devices form the backbone of modern botnets. Millions of end-of-life devices that no longer receive patches remain connected to the internet, creating a permanent pool of targets for botnet malware. Until manufacturers and users take responsibility, the supply of infected devices will keep growing. Every unsecured device on the internet is a potential recruit for the next botnet. The problem is global, and it will not solve itself. Governments in several countries are starting to set minimum security standards for connected devices, but adoption is slow. In the meantime, the burden falls on users and IT teams to secure their own devices.

Signs Your Device May Be Part of a Botnet

Botnets are built for stealth. The bot herder wants your device to stay infected as long as possible, so botnet malware hides its tracks. Still, there are signs that can tip you off. If you notice any of these on your devices, investigate at once.

Slow performance: Your device runs much slower than normal, even when you are not using it. Botnet malware uses CPU, memory, and bandwidth in the background to carry out botnet attacks.
Strange network traffic: Unexpected spikes in outbound network traffic, especially to unknown IP addresses, suggest a bot is phoning home to its C2 server or joining an active attack.
High bandwidth use: Your internet connection is slower than usual, or your ISP warns you about unusual data use. Botnets use your bandwidth to send spam, launch DDoS floods, or relay stolen data.
Unknown processes: New or unfamiliar programs appear in your task manager. Botnet malware often runs as hidden services that start with your operating system.
Failed logins: You see login attempts or account lockouts you did not cause. This could mean your device is being used for brute force or credential stuffing as part of a botnet attack.

If you spot these signs, disconnect the device from the network and run a full malware scan. Early detection of botnet infections can prevent your device from being used in botnet attacks against others. The faster you find and clean a bot, the less damage it can do. Keep a log of any suspicious activity and share it with your security team right away. For broader guidance on keeping devices safe, see our article on endpoint security.

How Botnets Evade Detection

Modern botnets are built to stay hidden. The longer a device stays infected, the more value it provides to the attacker. Here are the main tricks that make detection so difficult.

Low-and-slow communication. Instead of sending large bursts of data, bots communicate with their C2 servers in small, timed packets that blend into normal traffic. This makes it hard for standard monitoring tools to flag the activity as suspicious. The traffic looks like regular browsing or DNS queries.

Domain generation algorithms (DGAs). Some bots use algorithms that create hundreds of random domain names each day. The C2 server registers just one of them. The bot cycles through the list until it finds the live one. This makes it nearly impossible to block the C2 channel by blacklisting a single domain. Security teams can counter this with DNS analytics that detect the random query patterns typical of DGA activity.

Advanced Hiding Techniques

Encrypted channels. Many bots encrypt their C2 traffic using HTTPS or custom encryption. This hides the content of the communication from network monitors. Without deep packet inspection or decryption at the network edge, this traffic passes through firewalls unnoticed.

Living off the land. Instead of installing new programs, some bots use tools already on the device, like PowerShell, WMI, or built-in scripting engines. Since these tools are legitimate, security software may not flag their use. This technique makes it harder to tell the difference between a bot and a normal user.

Understanding these evasion methods helps security teams tune their detection tools. Behavioral analysis, DNS analytics, and endpoint detection are more effective than signature-based scanning alone when dealing with advanced threats. Layered monitoring is the key to catching bots that are designed to stay silent. Combine DNS query analysis with endpoint behavior tracking and threat feeds for the best results. Even when a single tool misses the signs, the combined data from multiple sources often reveals the pattern.

How to Defend Against Botnet Attacks

Stopping botnets requires action at every layer, from individual devices to the network edge. Here is a practical defense plan that covers the most important steps.

Step 1

Patch and Update Everything

Keep all operating systems, firmware, and applications up to date. Botnet malware exploits known flaws that vendors have already fixed. Enable automatic updates on all devices, especially internet of things iot devices like routers and cameras. Unpatched devices are the easiest entry point for botnet infections.

Step 2

Change Default Passwords

Replace every default username and password on every device. Botnets use brute force attacks with lists of default credentials to take over routers, cameras, and other connected hardware. Use long, unique passwords for each device. This single step blocks many botnet infections before they start.

Step 3

Monitor Network Traffic

Deploy network monitoring tools that watch for unusual outbound traffic patterns. Bots communicate with their C2 servers at regular intervals. Spotting this network traffic early lets you isolate infected devices before they join a botnet attack. Intrusion detection systems (IDS) can flag known botnet C2 signatures.

Step 4

Deploy Endpoint Protection

Install and maintain endpoint security tools on all devices. Good endpoint protection catches botnet malware before it installs. It also detects and removes bots that have already landed. Make sure your solution includes rootkit detection, since botnet malware often hides deep in the operating system.

Step 5

Segment Your Network

Separate internet of things iot devices from your main network. If a camera or router gets infected with botnet malware, network segmentation stops the infection from spreading to servers and workstations. This limits the damage any single botnet infection can cause to your organization.

For expert help building these defenses, our cybersecurity services team can assess your exposure and deploy the right tools.

How Law Enforcement Fights Botnets

Governments and law enforcement agencies around the world have made botnet takedowns a top priority. These operations target the C2 infrastructure, the bot herders behind them, and the infected devices themselves.

The 911 S5 botnet, once the world’s largest, was dismantled in a joint international operation. More recently, the US Department of Justice disrupted the Aisuru/Kimwolf botnet, which had grown to over 3 million infected devices and was responsible for the largest DDoS attacks ever recorded. Law enforcement worked with companies like Cloudflare, Lumen, and Google to null-route C2 servers and sinkhole infected devices.

However, botnet takedowns are not permanent solutions. New botnets rise to fill the gap quickly. The peer to peer architecture of modern botnets makes them harder to disrupt because there is no single server to seize. Furthermore, many bot herders operate from countries with weak cybercrime laws, making arrest and prosecution difficult. This is why defense at the device and network level remains essential. You cannot rely on law enforcement alone to stop botnet attacks. Defense must start at your own network edge and reach all the way down to every connected device. Think of law enforcement action as a helpful bonus, not a core plan. Your security posture should hold even if no takedown ever happens.

Understanding the broader threat landscape is key. For more on detection and response tools, see our guide to threat intelligence.

Botnets and Ransomware: A Growing Link

Botnets and ransomware are closely connected. Many ransomware attacks begin with a botnet infection. The bot herder uses the botnet to gain initial access to a target network, then drops ransomware on as many infected machines as possible. This two-stage approach lets attackers hit more targets with less effort.

Some botnets function as delivery platforms. Emotet, for example, delivered ransomware payloads like Ryuk and Conti to thousands of organizations worldwide. The botnet handled the hard work of getting past defenses, and the ransomware operators took over from there. This kind of teamwork between botnet operators and ransomware gangs has become a standard part of the cybercrime economy.

Consequently, defending against botnet infections is also a defense against ransomware. If you block the botnet at the door, you block the ransomware delivery channel too. Network segmentation, endpoint protection, and monitoring for C2 network traffic all serve double duty. A single investment in these controls protects you from both types of attacks at once. Organizations that treat these threats as separate problems spend more money and get weaker results. A unified approach to network defense is always smarter.

Notable Botnets in History

Some botnets have been so large and destructive that they shaped the way we think about cybersecurity. Here are a few that every IT professional should know about.

Mirai

The Botnet That Changed Everything

Mirai targeted internet of things iot devices with default passwords and launched massive DDoS attacks that knocked major websites offline. Its source code was later released publicly, spawning dozens of variants that still power botnet attacks today. Mirai proved that infected devices like cheap routers and cameras could generate devastating network traffic.

Emotet

The Malware Delivery Platform

Emotet started as a banking trojan but evolved into a full botnet malware delivery platform. It spread through phishing emails and sold access to other criminal groups. Law enforcement disrupted Emotet in a major operation, but it later came back in new forms. Emotet showed how botnets can steal sensitive information and deliver ransomware at the same time.

Aisuru / Kimwolf

Record-Breaking DDoS Power

The Aisuru botnet grew to over 3 million infected devices, mostly Android TVs and routers. It launched botnet attacks that reached 31.4 Tbps, the largest DDoS ever recorded. The US DOJ disrupted it in a multi-agency operation. Aisuru showed how quickly a botnet can grow when it targets cheap, unpatched internet of things iot devices with no security controls.

Botnet Detection and Response Tools

Catching botnet infections early is the best way to limit damage. Several types of tools help security teams find and remove bots from their networks.

Intrusion detection systems (IDS). These tools watch network traffic for patterns that match known botnet C2 communications. When a match is found, they raise an alert so security teams can investigate. An IDS with up-to-date threat signatures can spot many botnet infections the moment they phone home.

Endpoint detection and response (EDR). EDR tools run on each device and watch for suspicious behavior, like an unknown process trying to connect to an outside server. They can quarantine infected machines and remove botnet malware before it spreads. For a deeper look at detection tools, see our guide to endpoint detection and response.

Network-Level Detection Methods

DNS sinkholing. Security teams and law enforcement redirect botnet C2 domain lookups to a safe server. This cuts the connection between the bot and its bot herder, rendering the botnet useless without removing the malware from each device. DNS sinkholing is a key technique in large-scale botnet takedowns.

SIEM platforms. Security information and event management tools collect logs from across the network and correlate them to spot botnet activity. They can connect scattered signals, like a device making unusual DNS queries and sending data to a known bad IP, into a single alert. For more on how SIEM helps with detection, see our guide.

Key Takeaway

Botnets hide in plain sight. The best defense combines strong endpoint protection, constant network traffic monitoring, and updated threat intelligence. No single tool catches every botnet infection, but layered detection dramatically reduces the time a bot stays active on your network. The goal is to cut the dwell time from months to minutes. Every hour a bot stays active is an hour it can steal data, send spam, or join an attack.

The Future of Botnets

Botnets are evolving faster than ever. Several trends point to where the threat is headed and what defenders should prepare for.

AI-powered attacks. Attackers are starting to use artificial intelligence to make their botnets smarter. AI can help bots pick targets, adjust attack patterns in real time, and evade detection systems that rely on fixed rules. As AI tools become cheaper and easier to use, expect more attackers to adopt them. On the defense side, AI also helps by spotting anomalies in network traffic that human analysts would miss. The race between offensive and defensive AI will shape the threat landscape for years to come.

Larger and faster. The scale of attacks keeps growing. DDoS attacks that exceeded 1 terabit per second were rare just a few years ago. Now they are common. Botnets with millions of devices can generate traffic that overwhelms even the biggest cloud providers. The arms race between attackers and defenders will continue to push these numbers higher.

More IoT targets. The number of connected devices is expected to keep rising. Smart home gadgets, industrial sensors, medical equipment, and vehicles all offer new targets. Many of these devices have limited security and will remain vulnerable for years. They will provide a steady supply of recruits for future attacks.

The Rise of Criminal Bot Services

Criminal services model. Botnets are increasingly rented out as a service. Attackers who cannot build their own can pay for access to an existing network. This lowers the skill barrier and lets more criminals launch large-scale operations. The business model behind these services continues to mature, with pricing tiers, customer support, and even money-back guarantees.

Defenders who understand these trends can plan ahead. Investing in automated detection, network segmentation, and proactive patching will remain the best countermeasures. The threats will change, but the fundamentals of defense stay the same. Patch, monitor, segment, and train your team. These four actions will remain your best tools no matter how advanced or clever the threats become in the years ahead.

Frequently Asked Questions

What is a botnet?

A botnet is a network of infected devices controlled by a bot herder to carry out botnet attacks. The term botnet comes from “robot” and “network.” Botnets are used for DDoS attacks, spam campaigns, credential theft, and distributing botnet malware to new targets.

How do devices become part of a botnet?

Devices become part of a botnet when they are infected with botnet malware. This malware arrives through phishing emails, drive-by downloads, or brute force attacks on weak passwords. Internet of things iot devices are common targets because they often lack strong security controls.

Can a botnet be stopped?

Botnets can be disrupted through law enforcement takedowns, C2 server seizures, and DNS sinkholing. However, new botnets rise quickly. The best defense is to prevent botnet infections in the first place by patching devices, changing default passwords, and monitoring network traffic for signs of C2 activity.

What is a bot herder?

A bot herder is the attacker who builds and controls a botnet. The bot herder issues commands to all infected devices through a command-and-control server or peer to peer network. Bot herders use botnets to launch types of attacks like DDoS, data theft, and spam at massive scale.

Are IoT devices at risk of botnet infections?

Yes. Internet of things iot devices are among the most common targets for botnet infections. Routers, cameras, smart TVs, and other connected devices often ship with weak default passwords and rarely receive updates. These infected devices form the bulk of modern botnets.

Protecting Your Network from Botnet Threats

Botnets are one of the most persistent and fast-growing threats in cybersecurity. They turn everyday devices into weapons, using infected machines to launch botnet attacks at a scale that individual hackers could never achieve alone. The types of attacks that botnets enable, from distributed denial of service ddos attacks to data theft to spam, affect organizations of every size.

The good news is that botnet infections are preventable. Patch your devices. Change default passwords. Monitor your network traffic for C2 activity. Segment your internet of things iot devices from the rest of your network. Deploy endpoint protection that can catch botnet malware before it takes root. These steps are not complex, but they must be consistent. Gaps in coverage are exactly what attackers look for and exploit. One unpatched router or one device with a default password is enough for an attacker to get a foothold.

Botnets will keep evolving. New botnet malware will target new types of devices. Bot herders will find new ways to hide their C2 channels. However, the fundamentals of defense stay the same. Know how botnets work. Watch for the signs of botnet infections. Act fast when you find them. Every device you protect is one less bot in the next attack. The choices you make about patching, passwords, and monitoring shape whether your devices serve you or serve a criminal. Take control before a bot herder does. The investment in prevention is always far smaller than the cost of recovery after a successful attack. Start today, stay consistent, and build your defenses before the next wave arrives.

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What Is a Botnet? How Botnet Attacks Work and How to Stop Them