What is the Mirai Botnet? It’s a notorious strain of malware that transforms unsecured Internet of Things (IoT) devices, like cameras, routers, and DVRs, into zombie bots to conduct large-scale Distributed Denial of Service (DDoS) attacks.
First surfacing in 2016, Mirai stunned the cybersecurity world with its sheer scale, peaking with attacks that exceeded 1 Tbps.
The malware’s effectiveness lies in its ability to exploit default credentials on IoT devices, enabling attackers to hijack thousands, sometimes hundreds of thousands, of connected endpoints. Although Mirai’s original creators have been identified and prosecuted, the botnet’s source code was leaked online, fueling the creation of many new variants that remain active to this day.
Key Takeaways:
- Mirai exploits weak or default credentials in IoT devices.
- It has launched some of the largest DDoS attacks in history.
- Its publicly released source code spawned countless dangerous variants.
- Mitigation requires a multi-layered approach: securing IoT devices, changing default passwords, and implementing DDoS defenses.
What Is a Botnet and How Does It Work?
Before we dive deeper into Mirai, it’s essential to understand what a botnet is. A botnet (short for “robot network”) is a network of computers or devices infected with malware and controlled by an attacker, often without the users’ knowledge. These compromised devices, commonly referred to as bots or zombies, are utilized to execute coordinated cyberattacks.
Common purposes of botnets include:
- DDoS attacks (overloading services to shut them down)
- Spam campaigns
- Credential stuffing
- Click fraud
- Cryptomining (crypto-jacking)
Origins and Technical Overview of the Mirai Botnet
The Mirai Botnet was first identified in August 2016. It was created by three college students—Paras Jha, Josiah White, and Dalton Norman, who initially used it to attack rival Minecraft servers. Written in C for the bot client and in Go for the command-and-control (C2) infrastructure, Mirai gained notoriety after it was used in some of the largest DDoS attacks ever recorded.
Its infection cycle begins by scanning the IPv4 address space for devices with open Telnet ports (typically port 23 or 2323). Once it identifies a vulnerable device, it brute-forces its way in using a hardcoded list of default usernames and passwords. Upon a successful login, Mirai installs itself in memory, removes any existing malware, and reconnects to its command server to await further instructions.
What makes Mirai particularly dangerous is its simplicity. It doesn’t need advanced exploits or zero-day vulnerabilities. Instead, it exploits the most common oversight in IoT security: default credentials left unchanged. Once compromised, a device becomes part of a botnet that can be used to flood websites and services with malicious traffic. This attack method is what enabled the Mirai Botnet to take down major internet infrastructure in 2016.
Major Events and Impact
Mirai made global headlines when it launched a 620 Gbps DDoS attack against the website of security researcher Brian Krebs in September 2016. Shortly afterward, it unleashed an even more massive 1 Tbps attack on OVH, a French hosting company. The most far-reaching attack occurred in October 2016, when the Mirai Botnet targeted Dyn, a major DNS provider. The assault rendered popular websites like Twitter, Netflix, Reddit, and PayPal temporarily inaccessible across large swaths of the United States and Europe.
Here is a brief timeline of the most critical events:
- August 2016: Mirai surfaces and begins scanning for vulnerable IoT devices.
- September 2016: 620 Gbps attack on KrebsOnSecurity.
- October 2016: Dyn DNS attack knocks out major websites across the U.S. and Europe.
- November 2016: The malware causes major disruptions for UK ISPs, including TalkTalk.
- December 2016: Mirai creators are identified and plead guilty. The source code is publicly released.
The public release of Mirai’s source code was a turning point. Cybercriminals began creating their own versions of Mirai, some incorporating zero-day vulnerabilities and targeting specific devices like routers and IP cameras. Today, numerous Mirai variants exist, including Satori, Okiru, and Hakai, many of which are still actively used in attacks.
How the Mirai Botnet Works
Mirai’s infection cycle is surprisingly straightforward. It begins with a scanner component that probes random IP addresses for open Telnet ports. Once it finds a live system, it attempts to log in using a built-in list of over 60 commonly used default usernames and password combinations. If the login is successful, the malware binary is downloaded onto the device and added to the botnet.
Once a device is part of the botnet, it becomes a soldier in large-scale DDoS attacks. Mirai supports multiple attack vectors, including UDP floods, TCP SYN floods, and HTTP application-layer attacks. The command-and-control servers then direct the infected devices to flood a target server or service with traffic, overwhelming it and rendering it unavailable.
Mirai also includes code to eliminate rival malware from the device, ensuring exclusive control. While the original version of Mirai employed a centralized C2 architecture, later variants have evolved to adopt peer-to-peer systems, making them more resilient to takedown.
Continued Relevance in Modern Cybersecurity
Despite being nearly a decade old, Mirai remains a serious threat. Its code is still widely available and easily adaptable, which is why new variants continue to emerge. Furthermore, the IoT ecosystem remains vulnerable, mainly because many manufacturers still ship devices with default credentials and poor security configurations. Many IoT devices cannot receive firmware updates or are rarely updated by users, making them easy targets for botnets.
Mirai serves as a cautionary tale and a blueprint for how simple security oversights can have massive global consequences. As the number of connected devices continues to grow—expected to surpass 25 billion by 2030—the potential for similar or even more destructive botnets is increasing. This makes understanding Mirai crucial for network defenders and IT teams tasked with securing infrastructure.
How to Defend Against Mirai and Its Variants
Preventing Mirai infections requires a combination of good device hygiene and robust network defenses. First and foremost, users must change default usernames and passwords on all connected devices. Disabling unused services like Telnet and SSH can further reduce the attack surface. Devices should be regularly updated with the latest firmware to patch known vulnerabilities.
From a network perspective, implementing VLANs to isolate IoT devices from critical systems can limit the damage if a device is compromised. Organizations should also deploy DDoS mitigation services, which can absorb or reroute malicious traffic before it reaches its target. Ingress and egress filtering can help prevent compromised devices from communicating with command-and-control servers.
Below is a quick checklist for mitigating Mirai-based threats:
- Change all default credentials on IoT devices.
- Disable unnecessary remote services like Telnet.
- Regularly update device firmware.
- Use network segmentation to isolate IoT devices.
- Deploy DDoS protection and traffic monitoring tools.
- Implement ingress and egress filtering at the network edge.
Are Mirai Variants Still a Threat Today?
Following the release of the original Mirai code, numerous variants emerged. Some of the most notable include Satori, which exploits vulnerabilities in Huawei routers, and Okiru, which targets ARC processors used in embedded devices. Other derivatives, such as Hajime and Mozi, utilize peer-to-peer architectures to prevent centralized shutdowns. These variants often include more advanced features, such as encryption, zero-day exploits, and even ransomware components.
The continuous evolution of Mirai derivatives highlights the enduring nature of the threat. As long as insecure IoT devices remain connected to the internet, Mirai and its descendants will continue to pose risks.
Here is a viral video, ‘The Untold Story of Three Young Hackers and the Weakness of Cybersecurity,’ which answers the question of whether Mirai variants are still a threat today.
Final Thoughts?
So, what is the Mirai Botnet? It’s a stark reminder of the dangers posed by unsecured IoT devices and the far-reaching consequences of poor cybersecurity practices. From its humble beginnings as a tool for knocking rivals offline in the gaming world to its role in taking down portions of the internet, Mirai has left a lasting legacy. The continued emergence of Mirai variants underscores the need for better device security, vigilant network monitoring, and a proactive approach to threat mitigation. While the original threat actors have been brought to justice, the code they unleashed lives on—and so must our defenses.
For more insights into current cybersecurity trends and best practices, visit our Cybersecurity Blog, where we regularly post threat breakdowns, secure coding tips, and IT defense strategies.
Frequently Asked Questions
What is the Mirai Botnet, and how does it work?
The Mirai Botnet is malware that infects Internet of Things (IoT) devices using default login credentials. It turns them into bots used to launch massive Distributed Denial of Service (DDoS) attacks, overwhelming websites and services with malicious traffic.
Why was the Mirai Botnet so effective?
Mirai was highly effective because it exploited the widespread use of default usernames and passwords on IoT devices. Its simplicity, combined with the sheer number of vulnerable devices, enabled it to build large botnets quickly.
Is the Mirai Botnet still active today?
Yes, while the original Mirai creators were prosecuted, its source code was released publicly. This has led to the development of many active variants that continue to target vulnerable devices globally.
How can I protect my IoT devices from Mirai?
To protect against Mirai, change all default device passwords, disable unnecessary services such as Telnet, regularly update firmware, and isolate IoT devices from your primary network.
What were the biggest attacks caused by the Mirai Botnet?
Mirai was responsible for several record-breaking DDoS attacks, including a 1 Tbps attack on OVH and the October 2016 Dyn DNS attack, which disrupted major websites such as Twitter, Netflix, and PayPal.