botnet

What Is a Botnet? How Networks of Hijacked Devices Work (2026)

secure-os· Updated June 23, 2026· 4 min read #botnet#malware#ddos#security#iot

A glowing 3D mesh network of connected nodes, representing a botnet

Some malware does not want to harm your computer at all — it wants to recruit it. A botnet turns thousands or millions of infected devices into a remote-controlled army, usually without their owners ever noticing. This guide explains what a botnet is, how it works, what attackers do with one, and how to keep your devices out of it.

The short answer

A botnet is a network of internet-connected devices that an attacker secretly controls.
The name combines “robot” and “network” — each infected device is a bot that quietly obeys commands.
The owners almost never know: a botnet is built to stay hidden and use a small slice of each device.
Targets are not just PCs — phones, routers, and smart-home (IoT) gadgets are all recruited.

How a botnet works

A botnet starts with infection. A device catches malware — through a bad download, a weak password, or an unpatched flaw — that quietly enrolls it. From then on, the device checks in with a command-and-control server (or a peer-to-peer network) run by the attacker, who is called the bot-herder. When the herder sends an order, every bot acts at once. The power comes from scale: one attacker, millions of devices, all on command.

Rows of servers and cables in a data centre — A bot-herder sends one command and thousands of hijacked devices act together — that coordinated scale is what makes a botnet dangerous.

What botnets are used for

A botnet is a rented engine for large-scale abuse:

DDoS attacks — flooding a website with traffic from every bot at once to knock it offline.
Spam and phishing — sending huge volumes of email from many addresses to dodge filters.
Credential stuffing and fraud — testing stolen passwords or clicking ads at massive scale.
Spreading more malware — using infected devices to infect others and grow the network.

Many botnets are simply rented out to whoever pays, which is why a single one can do all of the above.

Signs and how to stay out of one

Because a botnet stays quiet, the clues are subtle: a device that feels slow or hot when idle, a home internet connection that lags for no reason, or a router behaving oddly. Keeping your devices out of a botnet is mostly good hygiene. Update everything, especially routers and IoT gadgets. Change default passwords — weak defaults are how most IoT bots are recruited. Run security scans for malware and rootkits, and do not install software from sources you do not trust.

The bottom line

A botnet is a hidden network of hijacked devices that one attacker controls to launch DDoS attacks, send spam, and commit fraud at enormous scale. Your phone, PC, or router can be drafted into one without a single visible symptom. The defense is unglamorous but effective: keep everything updated, replace default passwords, scan for malware, and install only what you trust — so your devices stay yours.

Frequently asked questions

What is a botnet in simple terms?

A botnet is a group of internet-connected devices that an attacker secretly controls all at once. Each infected device is a “bot” that quietly follows commands while its owner keeps using it normally. The attacker uses the combined power of thousands or millions of devices to launch attacks, send spam, or commit fraud — far more than any single machine could.

How does a device join a botnet?

It gets infected with malware, usually through a malicious download, an unpatched security flaw, or a weak or default password. This is especially common on routers and smart-home (IoT) devices that ship with easy-to-guess logins. Once infected, the device quietly contacts the attacker’s command server and waits for orders, all without any obvious sign to the owner.

How do I know if my device is part of a botnet?

The signs are indirect because botnets stay hidden. Watch for a device that runs slow or hot while idle, unusually high network activity, a sluggish home connection, or security software that has been switched off. None proves an infection alone, but together they justify a full malware scan and checking that your router’s firmware and passwords are up to date.

How can I protect my devices from botnets?

Keep everything updated, especially routers and IoT gadgets, and always change default passwords to strong, unique ones. Run regular security scans for malware, and only install software from trusted sources. These basic habits block the most common ways devices are recruited, keeping your phone, computer, and home network out of a botnet.