What is Internet Relay Chat (IRC)?
Internet Relay Chat (IRC) is a real-time text-based communication protocol designed for group discussions and one-to-one messaging over the internet. Introduced in the late 1980s, IRC was originally created to support open communication across distributed networks and quickly became popular among technical communities, developers, and early internet users.
From a cybersecurity perspective, IRC is best known for its historical role as a command-and-control (C2) mechanism for malware and botnets. While modern malware families increasingly rely on web-based APIs, social platforms, or custom encrypted channels, IRC continues to appear in threat campaigns due to its simplicity, flexibility, and low operational overhead.
Today, IRC remains relevant not because of its popularity among users, but because it demonstrates how lightweight communication protocols can be repurposed as reliable control channels for large-scale malicious activity.
How IRC Works (High-Level)
IRC uses a client–server architecture. Users connect to an IRC server, which may be part of a larger IRC network. Once connected, users can join channels (chat rooms) or send private messages to other users.
Core elements of IRC include:
- IRC clients, which send and receive messages
- IRC servers, which route messages between clients
- Channels, which host group conversations
- Nicknames, which identify users
Communication relies on simple text-based commands such as JOIN, PRIVMSG, and QUIT. This minimalism makes IRC easy to implement, script, and automate.
Because IRC requires very little bandwidth and processing power, thousands of clients can remain connected simultaneously with minimal infrastructure, a property that attackers have historically exploited.
Despite its declining mainstream popularity, IRC is still used legitimately in several contexts:
- Open-source project collaboration
- Developer community discussions
- Technical support channels
- Private internal chat networks
These legitimate uses mean IRC traffic is not inherently malicious. However, in many enterprise environments, IRC is unnecessary for business operations, making it easier to treat as high-risk or suspicious traffic.
IRC was one of the earliest protocols adopted by botnet operators because it offers:
- Simple setup and configuration
- Real-time command distribution
- Centralized control through channels
- Easy automation through scripts
- Low bandwidth requirements
An attacker can configure a malware sample to automatically connect to a specific IRC server and channel, wait for instructions, and execute received commands. This model requires little custom development and works reliably across many networks.
In an IRC-based C2 model, infected machines (bots) behave as IRC clients. After infection, each bot connects to a predefined IRC server and joins a designated channel.
The attacker, acting as an IRC operator or privileged user, issues commands into the channel. All connected bots receive and execute those commands simultaneously.
Typical C2 functions include:
- Launching DDoS attacks
- Downloading additional malware
- Updating configuration files
- Stealing data and credentials
This centralized broadcast model allows attackers to control large botnets with minimal effort.
IRC-controlled botnets have historically been used for:
- Distributed denial-of-service (DDoS) attacks
- Spam campaigns
- Phishing distribution
- Credential harvesting
- Malware propagation
Among these, DDoS attack orchestration remains one of the most common uses.
When an attacker issues a DDoS command via IRC, all connected bots begin sending traffic toward the specified target. Depending on bot capabilities, attack types may include:
- TCP SYN floods
- UDP floods
- HTTP floods
- Reflection or amplification attacks
Because commands propagate in real time, attackers can rapidly start, stop, or modify attacks, making mitigation more challenging.
Although many modern botnets now use HTTP(S), peer-to-peer, or custom protocols, IRC-based control channels still appear in commodity malware and older botnet variants.
Signs that may indicate IRC-based malware include:
- Outbound connections to IRC ports (e.g., 6667)
- Persistent connections to unfamiliar external servers
- Suspicious nicknames or channel names
- Encrypted or obfuscated IRC sessions
- Hosts generating traffic immediately after receiving IRC messages
These indicators become more meaningful when correlated with endpoint and network telemetry.
Allowing unrestricted IRC traffic can expose organizations to:
- Internal host compromise
- Participation in external attacks
- Data exfiltration
- Regulatory and compliance exposure
- Lateral movement within networks
For many organizations, blocking IRC at the perimeter introduces little operational risk.
- Block or restrict IRC ports and protocols
- Implement network egress filtering
- Monitor outbound connections for anomalies
- Deploy behavior-based DDoS protection
- Maintain endpoint security and patching
- Correlate network and endpoint telemetry
- Network-layer anomaly detection
- Protocol-aware inspection
- Behavioral traffic analysis
- Upstream filtering and cloud scrubbing
- Continuous monitoring and alerting
Layered defenses are essential because IRC botnets often participate in multi-vector attack campaigns.
Radware DefensePro provides inline, behavior-based DDoS protection that detects attack traffic generated by IRC-controlled botnets, including SYN floods, UDP floods, and application-layer floods. DefensePro baselines normal traffic behavior and applies automated mitigation to block malicious sources while allowing legitimate traffic to pass.
Radware Cloud DDoS Protection Service offers high-capacity cloud-based scrubbing that absorbs large attack volumes before they reach on-prem or cloud environments, protecting bandwidth and upstream infrastructure during IRC-driven DDoS campaigns.
Threat Intelligence Subscriptions provide continuously updated intelligence on active botnet infrastructure and attacker sources, enabling proactive blocking of known malicious IPs associated with IRC-based threats.
Early botnets such as Agobot and SDbot relied heavily on IRC for command-and-control and were responsible for widespread DDoS and spam campaigns. While threat actors have since diversified their C2 methods, IRC-based botnets continue to surface in lower-complexity malware families and proof-of-concept tools.
Legacy protocols like IRC remain attractive to attackers because they are simple, well-understood, and easy to automate. Organizations should not assume that declining user popularity equates to declining threat relevance. Blocking unnecessary legacy protocols, combined with behavioral DDoS protection and threat intelligence, remains an effective way to reduce exposure.
To learn more about how Radware can safeguard your organization from IRC-driven botnets and DDoS attacks, contact us now.