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Discovered: February 19, 2003
Updated: February 13, 2007 11:43:19 AM
Also Known As: Backdoor.IRC.Cloner [KAV], TROJ_CLONER.DRP [Trend], Backdoor:IRC/Cloner [RAV]
Type: Trojan Horse
Systems Affected: Windows

Backdoor.IRC.Cloner is a backdoor Trojan that uses mIRC to communicate with a remote attacker. It allows the attacker to gain full control over your computer.

NOTE: Virus definitions dated prior to February 19, 2003 may detect some files in the Backdoor.IRC.Cloner package as IRC Trojan or BAT.Trojan.

Antivirus Protection Dates

  • Initial Rapid Release version February 19, 2003
  • Latest Rapid Release version November 04, 2019 revision 019
  • Initial Daily Certified version February 19, 2003
  • Latest Daily Certified version November 04, 2019 revision 065
  • Initial Weekly Certified release date February 19, 2003

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

Technical Description

Backdoor.IRC.Cloner typically arrives as a large executable file. The file is usually sent by email, but is sometimes sent through IRC.

When Backdoor.IRC.Cloner is executed, it typically performs the following actions:

  1. Creates a new subfolder in the %System% folder; although, some variants use %Windir%\System32. A typical name of this folder is %System%\Spool\Drivers\E3.

    • %Windir% is a variable. The Trojan locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt) and creates the folder in that location.
    • %System% is a variable. The Trojan locates the System folder and creates the folder in that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
  2. Inserts several files into the folder that the Trojan the created. Some examples of the file names are:
    • Abc.bat
    • Abc.dll
    • Abc.exe
    • Abcd.jpg
    • Attrib.exe *
    • Dtceindll32.dll
    • Hot.dll
    • Identd.exe *
    • Kill.exe *
    • Lsass.exe *
    • Moo.dll *
    • Psexec.exe *
    • Reg3.ocx
    • Regsvc.exe *
    • Remote.ini
    • Run32.bat
    • Set.bat
    • Shell32.bat
    • Shell32.dll

      NOTE: The files marked with an asterisk (*) are legitimate Windows or commercial files that Backdoor.IRC.Cloner has exploited. These files are not malicious, and as such, Symantec antivirus products do not detect them.
  3. Creates one registry value so that the Trojan is executed each time you start Windows. This value is typically located in either of these keys:


    The value added to the key will refer to one of the files within one of the folders (added by the Trojan). For example, one variant creates the value:

    MSKCES32 %windir%\System32\SPOOL\DRIVERS\E3\shell32.bat

    in the key:

  4. Logs into an IRC channel, through which the attacker can control the Trojan.

Other functionalities of Backdoor.IRC.Cloner include:
  • Uploading and downloading files to and from your computer
  • Executing programs and scripts on your computer
  • Flooding the IRC channels
  • Flooding mailboxes (mailbombing)
  • Opening a listening port on your computer, such as port 65,004
  • Connecting through port 6,667 to IRC
  • Initiating a copy functionality, whereby Backdoor.IRC.Cloner will try to copy itself to and execute on another computer on your network, if that particular computer has an open share that is protected with an easily guessed password.


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.


These instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Update the virus definitions.
  2. Restart the computer in Safe mode.
  3. Run a full system scan and delete all the files detected as Backdoor.IRC.Cloner. Delete folders that the Trojan added.
  4. Delete the value that the Trojan added to the registry.

For specific details on each of these steps, read the following instructions.

1. Updating the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain the virus definitions. These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate), in the "Protection" section, at the top of this writeup.
  • Downloading the definitions using the Intelligent Updater. The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater), in the "Protection" section, at the top of this writeup.

    The Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

2. Restarting the computer in Safe mode
All the Windows 32-bit operating systems, except Windows NT, can be restarted in Safe mode. For instructions on how to do this, read the document, "How to start the computer in Safe Mode ."

3. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with Backdoor.IRC.Cloner, write down the file name and location, and then click Delete.
  4. Using Windows Explorer, delete any subfolders added by the Trojan.

4. Deleting the value from the registry

CAUTION : Symantec strongly recommends that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.
  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type regedit

    Then click OK. (The Registry Editor opens.)
  3. Navigate to each of these keys:

  4. In the right pane, delete the value that refers to the file that was detected as the Trojan.
  5. Exit the Registry Editor.

Writeup By: Atli Gudmundsson