What Is a Botnet? How Infected Networks Attack

Understanding Botnets: The Criminal Internet Within the Internet

A botnet is a network of internet-connected devices — computers, smartphones, routers, cameras, smart TVs, and other IoT devices — that have been secretly infected with malware and placed under the control of a cybercriminal called a "bot herder" or operator. Each infected device is called a "bot" or "zombie."

The infected devices continue to function normally for their legitimate users, making detection difficult. The malware operates silently in the background, awaiting instructions from the operator. The bot herder can direct thousands or millions of bots simultaneously, providing enormous computing power and bandwidth that can be rented out or weaponized for criminal purposes.

Botnets are the backbone of the modern cybercrime economy. They're responsible for the majority of spam email globally, most DDoS attacks, large-scale credential stuffing operations, ad fraud (generating fake clicks to steal advertising revenue), cryptocurrency mining, and financial fraud. The Mirai botnet, which infected IoT devices with weak or default passwords, generated record-breaking DDoS attacks exceeding 1 Tbps in 2016.

Scale provides power. What one computer can't accomplish — whether sending millions of emails without triggering spam filters, overwhelming a server with requests, or trying billions of password combinations — tens of thousands of distributed bots can do efficiently and cheaply.

How Devices Become Infected

Phishing emails are the most common infection vector for personal computers. A convincing email containing a malicious attachment (document with macros, ZIP with executable, PDF exploit) or a link to a drive-by download site infects the machine when opened. Modern botnets use polymorphic malware that continuously mutates to evade signature-based antivirus detection.

Drive-by downloads exploit vulnerabilities in web browsers, browser plugins (Flash, Java, PDF readers), or unpatched OS components. Visiting a compromised or malicious website can silently install a bot without any user interaction — just loading the page is enough if your software is outdated.

IoT vulnerabilities are an epidemic. Routers, IP cameras, smart doorbells, and NAS devices often ship with default credentials (admin/admin, admin/password) that are never changed. They run outdated Linux kernels with known vulnerabilities and rarely receive automatic security updates. Mirai-family malware actively scans the internet for such devices using tools like Shodan to build massive botnets from smart home devices.

Supply chain attacks insert malware into legitimate software before distribution. The SolarWinds attack injected bot code into a trusted IT management tool, infecting thousands of organizations including US government agencies. These attacks are particularly dangerous because the user's trust in the software is exploited.

Check your public IP address for unusual behavior patterns and run a port scan on your home network to identify any unexpectedly open services that might indicate a compromised device.

Botnet Command and Control (C2) Architecture

Early botnets used centralized command-and-control servers that bots connected to for instructions. This architecture was simple to build but fragile — taking down the C2 server disabled the entire botnet. Law enforcement and researchers used sinkholing (redirecting C2 domain traffic to monitoring servers) to disrupt these operations.

Modern botnets use peer-to-peer (P2P) C2 architectures where each bot acts as both client and server, relaying instructions through the network. There's no single point of failure; taking down individual nodes doesn't disable the botnet. ZeuS, GameOver Zeus, and the Kelihos botnet all used P2P architectures.

Even more resilient are botnets using Domain Generation Algorithms (DGAs). The malware generates hundreds of pseudo-random domain names per day, and the operator registers just one of them to issue commands. Defenders must predict and pre-register all possible domains to disrupt communication — an enormous task.

Recent botnets have moved to encrypted C2 channels over HTTPS and even legitimate platforms like Twitter, Discord, Pastebin, and GitHub. Commands are embedded in posts or files on these platforms, making them nearly impossible to block without disrupting legitimate services. This technique is called "living off the land" for C2 infrastructure.

How to Detect and Remove Botnet Malware

Behavioral indicators are often more reliable than signature-based detection. Watch for unusual network activity: unexpected outbound connections (especially to foreign IPs on non-standard ports), sustained high CPU usage at idle, disk activity with no apparent cause, and unusual processes in the task manager or activity monitor.

Network-level detection is more powerful. Monitor your router's outbound traffic — most home routers can display connected devices and their bandwidth usage. Unexpected large data transfers, connections to unusual countries, or outbound SMTP traffic from non-mail devices are strong indicators of botnet activity.

For removal: boot from a clean USB with antimalware tools (Malwarebytes, Kaspersky Rescue Disk), scan in an environment where the malware can't protect itself. For router and IoT devices, perform a factory reset and immediately change default credentials before reconnecting to the internet. Update all firmware before enabling internet access on IoT devices.

Check whether your IP has been flagged on any botnet-related blacklists — AbuseIPDB, CBL, and Spamhaus XBL specifically track botnet-compromised IPs. Finding your IP on these lists is a strong indicator your network has been compromised.

Frequently Asked Questions