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Discovered: May 02, 2003
Updated: May 21, 2010 8:18:35 AM
Type: Trojan
Infection Length: Varies
Systems Affected: Windows

Backdoor.IRC.Bot is a generic detection for Trojan horses that open a back door on the compromised computer and connect to Internet Relay Chat (IRC) channels to launch distributed denial of service (DDoS) attacks.

A Backdoor.IRC.Bot is a type of Trojan that it also often referred to as a 'bot' that opens a back door that allows a remote attacker to take control of the compromised computer.

The actions a remote attack can perform on the compromised computer are numerous. It can also use the compromised computer, usually in a network of other compromised computers, called a botnet, to attack other targets.

The malicious author may build a botnet for various reasons but the underlying motivation is to accomplish a task or tasks that are done easier and/or faster with many computers rather than just one.

They may also perform actions that mislead the user into thinking that nothing untoward is happening on the computer when in fact the Trojan may have already opened a back door and be under the control of the remote attacker.

If a Symantec antivirus product displays a detection alert for this threat, it means the computer is already protected against this threat and the Symantec product will effectively remove this threat from the computer.

Antivirus Protection Dates

  • Initial Rapid Release version May 02, 2003
  • Latest Rapid Release version July 26, 2019 revision 021
  • Initial Daily Certified version May 02, 2003
  • Latest Daily Certified version July 27, 2019 revision 002
  • Initial Weekly Certified release date May 07, 2003

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Technical Description

Backdoor.IRC.Bot is a generic detection for Trojan horses that open a back door on the compromised computer and connect to Internet Relay Chat (IRC) channels to launch distributed denial of service (DDoS) attacks.

Background information

A Backdoor.IRC.Bot is a type of Trojan horse that opens a back door on the compromised computer using Internet Relay Chat (IRC) channels, allowing a remote attacker to perform various functions. In particular, this type of Trojan - also known as a 'bot' as it allows the attacker to gain control of the compromised computer - creates a type of network of computers, called a botnet , to launch distributed denial of service (DDoS) attacks at a specific target.

A malicious author creates the Trojan and distributes it using a variety of methods, such as placing it on peer-to-peer websites or spamming it as an email attachment. (Its worth remembering that Trojans do not self-replicate, hence the malicious author needs to utilize other vehicles for it to spread.) Once the threat has compromised a computer, it joins a predetermined IRC channel and awaits instructions from the malicious author. As this process is completed almost, if not completely, silently - for example, the Trojan may have been bundled with a video file and while that video plays normally, the Trojan is installed in the background - the user is unaware that his or her computer has been compromised and that a back door is now open.

Once the malicious author has compromised multiple computers and built the botnet - there have been cases of botnets containing tens of thousands of computers - the author will issue commands for the botnet to perform a DDoS attack. A denial of service is as the name suggests, whereby the target server is overwhelmed by numerous simultaneous connection requests, therefore denying access to any new connections.

Why carry out a DDoS attack?
The target can be virtually any server but typically is a website that the malicious author would like to disrupt for political purposes or monetary gain. A site can be brought down and amongst the confusion of trying to restore it, the attacker may gain access to the site without the site administrators noticing. Once in, the attacker may steal, delete, or replace information.

Are there any other uses for a botnet?

Botnets can be used in various ways other than just carrying out DDoS attacks and generally have one thing in common: financial gain. These methods are varied, but include such things as spamming, installing adware or spyware, hosting fraudulent banking websites, extortion (attackers can either threaten to unleash a DDoS on a company’s website unless a ransom is paid or hold a company’s files hostage and threaten to destroy them), or instruct the botnet to click on pay-per-click banner ads.

Who creates botnets?
As there is significant financial gain from operating a botnet, not only individuals but criminal organizations have been known to create botnets.

Are there any tell-tale signs?
Back door Trojans are generally discrete programs that attempt to mask their true purpose by masquerading as other software in the classic sense of the term Trojan horse. Some may run as advertised, that is as a video or some other program, others may display a fake error message, and others still may seemingly do nothing at all. However, they all have one thing in common: in the background the threat is executed.

As the threat runs silently, there are few signs of infection but nonetheless there are indeed signs. They may include registry changes or other system configuration changes after the threat has been installed. Another tell-tale sign is if connections are being made to unexpected and/or unknown locations. Possible the most noticeable sign of infection is if a user notices a distinct and unexpected slow-down in Internet speed.

What other actions can an attacker perform on a compromised computer?

The following is a list of some of the actions that Backdoor.IRC.Bot can perform:

  • Listening on an IRC channel for commands from a remote attacker, allowing them to control a compromised computer
  • Connecting through a TCP port to an IRC server
  • Viewing system information, such as running processes, software installed, and other items
  • Ending processes
  • Flooding the IRC channels
  • Flooding mailboxes (mailbombing)
  • Executing programs and scripts on the compromised computer
  • Uploading or downloading files
  • Updating the Trojan
  • Searching for files on the compromised computer
  • Executing commands on

What are the risks?
As a remote attacker can take control of a compromised computer, the damage the attacker can do is virtually unlimited. However, the goal of the attacker is to stay undetected and therefore causing noticeable damage to the computer is counterproductive to this goal.

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 download activities initiated by these types of malicious programs. Program controls such as those found in Symantec Endpoint Protection can also help to prevent 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.


You may have arrived at this page either because you have been alerted by your Symantec product about this risk, or you are concerned that your computer has been affected by this risk.

Before proceeding further we recommend that you run a full system scan . If that does not resolve the problem you can try one of the options available below.

If you are a Norton product user, we recommend you try the following resources to remove this risk.

Removal Tool

If you have an infected Windows system file, you may need to replace them using from the Windows installation CD .

How to reduce the risk of infection
The following resources provide further information and best practices to help reduce the risk of infection.

If you are a Symantec business product user, we recommend you try the following resources to remove this risk.

Identifying and submitting suspect files
Submitting suspicious files to Symantec allows us to ensure that our protection capabilities keep up with the ever-changing threat landscape. Submitted files are analyzed by Symantec Security Response and, where necessary, updated definitions are immediately distributed through LiveUpdate™ to all Symantec end points. This ensures that other computers nearby are protected from attack. The following resources may help in identifying suspicious files for submission to Symantec.

Removal Tool

If you have an infected Windows system file, you may need to replace them using from the Windows installation CD .

How to reduce the risk of infection
The following resource provides further information and best practices to help reduce the risk of infection.
Protecting your business network

The following instructions pertain to all current Symantec antivirus products.

1. Performing a full system scan
How to run a full system scan using your Symantec product

2. Restoring settings in the registry
Many risks make modifications to the registry, which could impact the functionality or performance of the compromised computer. While many of these modifications can be restored through various Windows components, it may be necessary to edit the registry. See in the Technical Details of this writeup for information about which registry keys were created or modified. Delete registry subkeys and entries created by the risk and return all modified registry entries to their previous values.

Writeup By: Jarrad Shearer