A beginner-friendly, technically deep breakdown of the Mirai botnet written by a security researcher who was confused about it too. Six blogs. Real source code. No assumptions.
Read The Series
Blog 1 - From Zero to Botnet: What Is a Botnet and Why Should You Care?
Start here. This blog builds everything from the ground up no prior knowledge needed. You’ll learn what a botnet actually is through a story about a $15 security camera in Vietnam, how an army of 600,000 devices formed without their owners knowing, and what a C2 (Command and Control) server is and why it’s the brain of the operation.
What you’ll learn: Botnet, C2 server, bot, infection, spreading, DDoS basics, why volume beats security.
Blog 2 - How Mirai Actually Infects a Device
Who actually installs the malware? (Spoiler: not the bot that found the victim.) This blog breaks down the full infection chain from the SYN scan that finds vulnerable devices, to the staged Telnet login conversation, to the clever trick Mirai uses to detect which CPU the victim is running, to why deleting itself is the first thing the malware does.
What you’ll learn: SYN scanning, Telnet login stages, the Report Server, the Loader, ELF headers, CPU architecture detection, why disk deletion doesn’t stop a running process.
Blog 3 - I Opened Mirai’s Source Code. Here Is What I Found.
The first time reading actual malware source code line by line. Starting with main.c, the entry point of every C program. This blog walks through exactly what Mirai does in the first seconds after infection: delete itself, disable the hardware watchdog, hide its process name with random garbage, enforce single-instance control, then load weapons, kill competing malware, and start scanning. Each step deliberately chosen.
What you’ll learn: unlink(), watchdog timers, process name hiding, ensure_single_instance(), attack_init(), killer_init(), scanner_init(), the infinite C2 loop.
Blog 4 - Inside scanner.c: The Infection Engine
(Coming soon)
A deep dive into the scanner module how Mirai generates random IP addresses, which ranges it deliberately skips (and why), the 63 default credentials hardcoded into the source, and the state machine that tracks hundreds of simultaneous Telnet conversations without losing track of any of them.
Blog 5 - I Read the Brain of Mirai: How the C2 Server Actually Works
The C2 server written in Go, managing tens of thousands of bots simultaneously. This blog unpacks how one port handles both bot check-ins and attacker logins (using a 4-byte handshake), how the heartbeat system detects dead bots, what the attacker sees on their screen (including a live bot counter updating every second), and how attack commands get compressed into just 16 bytes before flying out to 50,000 devices at once.
What you’ll learn: Port 23 dual-purpose, bot handshake (00 00 00 [id_len]), heartbeat every 60 seconds, MySQL database structure, 16-byte attack packet format, the 10 attack type plugin system, Go goroutines for concurrency.
Blog 6 - Mirai’s Weapons: How 600,000 Cameras Brought Down the Internet
The DDoS engine where the army goes to war. Ten attack types, each designed to defeat a different defense. UDP flood with packet randomization to defeat firewalls. SYN flood that weaponizes correct TCP behavior. ACK flood that exploits stateless firewall blindness. HTTP flood with fake browser identities that Cloudflare can’t easily block. DNS water torture that makes innocent DNS servers do the attacking. And the fork() trick that lets one infected camera run an attack while staying connected to C2 simultaneously. This is the blog that explains the October 21, 2016 Dyn DNS attack 1.2 Tbps, Twitter and Netflix offline, the largest DDoS in history at the time.
What you’ll learn: Bandwidth exhaustion vs. connection exhaustion, UDP flood, SYN flood, ACK flood, HTTP Layer 7 flood, DNS water torture, GRE encapsulation, VSE amplification, fork() for parallel processes, attack_init() plugin architecture, the Dyn DNS attack.
Blog 7 - After Mirai: The Variants, The Copycats, and What Comes Next
(Coming soon)
What happened after the source code was released publicly and why releasing it was likely a calculated strategy, not a mistake. Dozens of Mirai variants. New targets. Modern IoT security implications.
Quick Reference
| Blog | Title | Status |
|---|---|---|
| 1 | What Is a Botnet? |  Published |
| 2 | How Mirai Infects a Device | Published |
| 3 | Inside main.c (Source Code) | Published |
| 4 | Inside scanner.c (Infection Engine) |  Coming Soon |
| 5 | How the C2 Server Works | Published |
| 6 | Mirai’s Attack Weapons | Published |
| 7 | After Mirai: Variants and Copycats | Coming Soon |
Tags
mirai · botnet · iot-security · ddos · malware-analysis · source-code · c2-server · router-exploitation · telnet · cybersecurity
Published on IoTSec Forum - IoT & Embedded Security Category