1. Symantec/
  2. Security Response/
  3. IRC Trojan

IRC Trojan

Risk Level 1: Very Low

June 16, 1998
June 7, 2007 9:58:19 PM
Infection Length:
Systems Affected:
Background information
Threats that utilize IRC have been around for a long time and have gone through some changes over the years. In the past, such threats would require a computer with an IRC client previously installed in order to function. Later iterations bundled a hacked copy of mIRC, a popular and readily available IRC client. Today, most IRC Trojan threats contain their own IRC client embedded within the Trojan.

What is IRC?
In a nutshell, Internet Relay Chat (IRC) is a computer network commonly used for communication, sharing files, and sending out distributed commands to computer networks. An IRC network is comprised of servers that contain “channels”, which are organized by topic. Threats like IRC Trojan use IRC to carry out back door functions.

For a more detailed description of IRC, see the Internet Relay Chat page on Wikipedia.

What does the Trojan do?
The primary purpose of IRC Trojan threats is to open a back door, allowing an attacker to issue commands to the compromised computer. While the functions that can be carried out are largely arbitrary (a back door generally provides full control of the computer), the following list highlights some functions that are often carried out by the back door in IRC Trojan threats:
  • Perform distributed denial of service (DDoS) attacks
  • Set up a proxy server to route traffic through the computer
  • Collect information (system and personal) from the computer and any storage device attached to it
  • Terminate or run tasks and processes
  • Download and execute additional files
  • Upload files and other content
  • Report on status
  • Open remote command line shells
  • Change computer settings
  • Shut down or restart the computer

Why would a Trojan use IRC?
Relaying the commands through an IRC server provides the attacker with a level of anonymity not as easily obtained by connecting directly to the threat’s back door. IRC also allows an attacker to control a large number of computers as a botnet. Since each threat compromised by a particular IRC Trojan threats logs into a predetermined IRC channel, an attacker can then send a command to the channel, and on to all the computers in the botnet.

Are there any tell-tale signs?
The default port for IRC communication is 6667, and server communication may utilize ports in the 6660-6669 range. However, IRC Trojan threats often use unusual port numbers to communicate with their IRC servers. Any unexpected IRC communication that falls outside of the standard realm should be regarded as suspicious. Firewalls or network monitoring tools may show network traffic to or from unusual remote addresses.

What are the risks?
The back door component of these Trojans pose a relatively high risk of damage or loss to the user if they can remain undetected and active for a significant time. On the lower end of the scale is annoyance through the loss of bandwidth or performance due to actions such as proxying traffic. On the upper end of the scale the risks include identity theft and the loss of money from online accounts due to the theft of login credentials.

What can I do to minimize the risks?
As a general rule, users should always run up-to-date antivirus software with real-time protection such as Norton Antivirus, Norton Internet Security, Norton 360 or Symantec Endpoint Protection. In addition, a firewall -- or better still, an Intrusion Prevention System (IPS) -- will help to block back channel activities initiated by these types of malicious programs. Program controls such as those found in Symantec Endpoint Protection can also help to prevent unknown programs such as these from executing in the first place.

How can I find out more?
Advanced users can submit a sample to Threat Expert to obtain a detailed report of the system and file system changes caused by a threat.


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
Writeup By: Ben Nahorney
Summary| Technical Details| Removal

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