What Is a Botnet? How They Work, Common Attacks, and How to Stay Safe

A botnet is a network of computers infected with malware and controlled remotely by an attacker, often without the owners ever noticing. The word combines “robot” and “network,” and that is exactly what it describes: a fleet of hijacked machines that follow orders from a single operator. If you have ever wondered what is a botnet and why security experts treat them as one of the biggest threats online, the short answer is scale. One infected device is a nuisance. Thousands working together can knock major websites offline.

Understanding what is a botnet matters because almost any device connected to the internet can be drafted into one — your laptop, your phone, your home Wi-Fi gear, even a smart camera. Below, we break down how botnets operate, the main attack methods they enable, and the simple habits that keep your devices off the roster.

What Is a Botnet, Exactly?

At its core, a botnet is a group of online machines that have been quietly taken over by malware. Each compromised device — sometimes called a “bot” or “zombie” — keeps running normally for its owner while secretly answering to a remote operator known as a bot herder. The herder issues instructions, and every machine carries them out at once.

The strength of a botnet comes from numbers. A single infected computer has limited power, but a herder controlling a large network of compromised computers can pool that power for tasks no individual machine could manage alone. This is why a botnet is the engine behind some of the most disruptive events on the internet.

What makes botnets dangerous is how invisible they are. Your device might be working for someone else right now and show nothing more than a slightly slower connection or unexplained activity in the background.

How Botnets Work

Building a botnet happens in stages. First comes the botnet infection: the attacker spreads malicious software through phishing emails, fake downloads, malicious websites, or unpatched software flaws. Once a user clicks a bad link or installs a tainted app, the malware quietly installs itself and the device joins the network.

After infection, the device reaches out to a control server to receive instructions. The bot herder — the hacker running the operation — uses this channel to send commands to the entire fleet, telling them when to attack, what to target, and when to go quiet. Many strains of botnet malware are built on a trojan horse model: the program looks harmless, so the user installs it willingly, and the trojan opens a back door for the attacker.

A botnet can lie dormant for weeks. The herder may simply wait, keeping the network ready until there is a reason to act — whether that means renting the botnet out to other cybercriminals or launching an attack of their own.

Botnet Architecture: The Models of Botnet Control

Not every botnet is wired the same way. There are two main ways an operator can control a botnet, and the difference shapes how hard each one is to shut down.

The first is the centralized model. Here, every bot connects back to a single command and control point — often called a C&C server. The herder sends commands from this hub, and the bots report back. Older botnets used Internet Relay Chat (IRC) for this; many modern IRC or HTTP botnets still rely on a centralized server because it is simple to manage. The weakness is obvious: take down that hub, and the whole botnet goes dark. It is a single point of failure that investigators love to target.

The second is the peer-to-peer model. In P2P botnets, there is no central hub. Instead of a clear client and a server relationship, each bot acts as both, passing instructions along to its neighbors. This design is far harder to dismantle because there is no single machine to seize — taking control of a botnet built this way means tracking down many nodes at once. Knocking out one node barely dents the network.

Understanding how the operator controls the botnet explains why some takedowns succeed quickly while others drag on for years. Whoever is operating a botnet picks the model that best balances control against the risk of getting shut down.

Types of Botnet Attacks

A botnet is a tool, and like any tool it can be pointed at many jobs. Here are several types of botnet attacks you should know about.

DDoS attacks. A distributed denial of service attack is the classic use case. The hacker orders every bot to flood a target server with requests at the same time, overwhelming it until legitimate visitors can no longer get through. Because the network can launch distributed denial-of-service traffic from thousands of devices at once, it is extremely difficult to block. A single botnet attack of this kind can take a major service offline for hours.

Spam and phishing. Botnets are perfect for sending mail in bulk. A herder can send spam from thousands of devices, slipping past filters that would flag a single source. Much of the world’s junk mail — and the phishing that rides along with it — flows through botnets rather than the attacker’s own machines.

Credential theft and fraud. Some botnets exist to steal sensitive information. They harvest login details, banking credentials, and saved passwords, then quietly ship that data back to the operator. Others run click fraud, faking ad clicks to drain advertising budgets and pad the attacker’s earnings.

Spreading more malware. A botnet can be used to distribute fresh malicious software to new victims, growing itself and seeding other attacks in the process. This is how hackers control their botnets at scale — each new infection adds another machine to the fleet.

If you want to understand the wider landscape these threats live in, our guide to what cybercrime is and how you can prevent it puts botnets in context alongside other digital threats.

IoT Botnets and the Mirai Example

For years, botnets were built from hijacked PCs. That changed with the rise of the Internet of Things. Smart cameras, routers, thermostats, and other internet-connected devices often ship with weak default settings and rarely get security updates, which makes them easy targets.

The most famous IoT botnet is Mirai. It scanned the web for gadgets still using factory default usernames and a known password list, then used those credentials to log in and take them over automatically. In 2016, the network grew large enough to launch one of the biggest DDoS attacks ever recorded, briefly disrupting major websites across the United States. The lesson was clear: a smart gadget left on default settings is an open door.

Another notorious case was once one of the largest spam engines on the planet before it was dismantled. Almost every popular botnet specializes in some way — some in spam, some in fraud, some in raw DDoS power, and large-scale botnet operations often combine all three.

How to Tell If You Are Part of a Botnet

A device caught in a botnet rarely announces itself, but there are signs of botnet activity worth watching for:

• Your device runs hot or slow for no clear reason, even when idle.
• Your internet connection feels sluggish because hidden background activity is eating your bandwidth.
• Programs crash, fans spin up, or your machine refuses to shut down properly.
• Your email contacts report messages you never sent.

None of these prove a compromise on their own, but together they are a reason to scan your system. Malware that turns a machine into a bot often arrives alongside other unwanted programs, so it is worth knowing how to remove spyware from a PC and how to spot a browser hijacker too.

How to Prevent Botnet Infections

You do not need expert skills to keep your devices safe. A few habits go a long way toward stopping the malware that tries to infect devices and pull them into a network:

• Update everything. Most botnet malware exploits known flaws that a patch has already fixed. Keep your operating system, apps, and router firmware current.
• Change default passwords. Replace every factory password on your gear with a strong, unique credential. Cutting off easy logins is the simplest way to deny an attacker the ability to control botnet members remotely.
• Be careful with links and attachments. Most infections start with phishing emails or a tainted download. Do not click or install from sources you do not trust.
• Run reputable security software. A good scanner catches the trojan horse before it can execute and call home to a control server.
• Lock down your network. Secure your home Wi-Fi, segment your IoT device collection, and protect your traffic on public networks, where attackers often try to gain access to unprotected connections.

A VPN plays a useful supporting role here. It encrypts your connection so attackers on the same network cannot easily intercept your traffic or harvest credentials, which is exactly the kind of opening many botnet operators look for.

Protect Your Devices with Planet VPN

Botnets thrive on exposed, unprotected connections — and a public Wi-Fi network is one of the easiest places for an attacker to snoop on your traffic or slip something malicious onto your device. Planet VPN helps close that gap.

With Planet VPN, your traffic is encrypted on every connection, so the data flowing to and from your devices stays private even on untrusted networks. The free plan gives you genuine core protection — encryption, a strict no-logs approach, and security on public Wi-Fi — with no time limits and no credit card required. If you want more locations, faster speeds, and extra features, Premium adds them on top — more, not a different kind of protection.

Ready to lock down your connection? Get Planet VPN and download it for your device in a couple of clicks.

Botnet FAQs

How do I know if I am in a botnet?

Watch for a device that runs slow or hot when idle, an internet connection that drags for no reason, programs that crash, or contacts reporting messages you never sent. These point to hidden background network traffic from a hidden compromise. The surest check is a full scan with reputable security software, which can detect the malware that turned your machine into a bot.

Is a botnet illegal?

Building, operating, or renting out a botnet is illegal in most countries, since it relies on infecting devices without consent and is used to carry out attacks like fraud and DDoS. Simply having an infected device does not make you a criminal — you are a victim, not the operator. The people who face charges are the ones who create and control the botnet.

Is a botnet good or bad?

A botnet is overwhelmingly bad. It exists to hijack other people’s devices and use their combined power for harmful ends — a DDoS attack, spam, credential theft, and more. The underlying idea of coordinating many computers is neutral and even used legitimately in research clusters, but the term “botnet” almost always describes a malicious network built without the owners’ permission.

What is meant by a botnet?

A botnet is a network of online devices infected with malware and controlled remotely by an attacker known as a bot herder. Each compromised device follows commands from a control server while still working normally for its owner. The herder uses the combined network to launch attacks, push out spam, or steal data.

What is a botnet example?

The best-known example is the Mirai botnet, which in 2016 infected hundreds of thousands of IoT devices — mostly cameras and routers left on default passwords — and launched record-breaking DDoS attacks. Another is the Grum botnet, which became one of the world’s largest spam operations before it was taken down by researchers and law enforcement agencies.

How do I remove a botnet?

Disconnect the infected device from the internet to cut its link to the attacker, then run a full scan with trusted antivirus or anti-malware software to find and remove the malicious code. Update your operating system and change your passwords afterward, since credentials may have been stolen. For stubborn infections, a factory reset is the surest fix. To avoid reinfection, keep your software patched and follow the prevention steps above.