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Discovered: November 09, 2003
Updated: February 13, 2007 12:13:37 PM
Type: Trojan Horse
Systems Affected: Windows

Backdoor.Exdis is a backdoor Trojan horse that allows a hacker to remotely control a computer through IRC.

Antivirus Protection Dates

  • Initial Rapid Release version November 10, 2003
  • Latest Rapid Release version July 09, 2018 revision 024
  • Initial Daily Certified version November 10, 2003 revision 002
  • Latest Daily Certified version July 10, 2018 revision 002
  • Initial Weekly Certified release date November 12, 2003

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

Writeup By: Heather Shannon

Discovered: November 09, 2003
Updated: February 13, 2007 12:13:37 PM
Type: Trojan Horse
Systems Affected: Windows

When the Trojan is executed, it performs the following actions:

  1. May be copied to the %Windir% folder as a random file name.

    • %Windir% is a variable. The Trojan can be found in the Windows installation folder (by default, this is C:\Windows or C:\Winnt).
    • The name and location of the file may be different, depending on the method by which the Trojan was placed on the computer.

  2. Sets the value:

    "(Default)"="ABCDEF %1 %*" (where ABCDEF represents the filename of the Trojan)

    in the registry key:


  3. If the operating system is Windows 2000/XP/NT, it will create a service for the Trojan and set it to automatically run. Known variants of this Trojan have used the following service names, but other names can be selected:
    • xd2s
    • xad2
    • xadx
    • xadz

  4. May create several non-viral files in the %System% folder, for example:
    • xad600.bin
    • execmd.xad
    • klg.dat
    • plg.dat
    • prtxad.bin
    • rasxad.bin

      Note: %System% is a variable. The Trojan locates the System folder and copies itself to 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).

  5. Connects to an IRC server and waits for commands. This backdoor can do the following:
    • View and kill processes
    • Upload and download files
    • Execute commands
    • Log keystrokes
    • Steal passwords
    • Act as an HTTP proxy
    • Send email from an infected computer


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: Heather Shannon

Discovered: November 09, 2003
Updated: February 13, 2007 12:13:37 PM
Type: Trojan Horse
Systems Affected: Windows

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

  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Restart the computer in Safe mode or VGA mode.
  4. Reverse the changes made to the registry.
  5. Scan for and delete files detected as Backdoor.Exdis.

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

1. Disabling System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article, "Antivirus Tools Cannot Clean Infected Files in the _Restore Folder," Article ID: Q263455.

2. 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 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).
  • 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).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Restarting the computer in Safe mode or VGA mode
Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.
  • For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
  • For Windows NT 4 users, restart the computer in VGA mode.

4. Reversing the changes made to the registry

WARNING: Symantec strongly recommends that you back up the registry before making 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. On the Desktop, double-click My Computer.

  2. Make sure that Windows is showing file extentions. In order to check this, do the following:
    1. Click the View menu (Windows 95/98/NT) or the Tools menu (Windows Me/2000/XP), and then click Options or "Folder options."
    2. Click the View tab.
    3. Click the Restore Defaults button.
    4. Click OK.

  3. Navigate to the following file, depending on your operating system:
    • Windows 95/98/Me/XP:

    • Windows NT/2000:

  4. Right-click on regedit.exe and select Rename.

  5. Type the following:

    and then press Enter.

  6. Double click

  7. Navigate to and select the key:


  8. In the right pane, double-click the (Default) value.

  9. Delete the current value data, and then type:

    "%1" %*

    That is, type the characters: quote-percent-one-quote-space-percent-asterisk.

  10. The next few steps depend on the operating system you are running.
    • If you are running Windows 95/98/Me, skip to step m.
    • Windows 2000/XP/NT only
      Navigate to each of these keys:


  11. From each one, delete any of these subkeys that you find:


  12. If none of these subkeys are found, the Trojan may be using a different service name. In which case, search the registry for references to the Trojan file:
    1. Click Edit > Find.

    2. In the "Find what" box, type:


    3. In the "Look at" section, make sure that the Values check box is selected. Deselect the Keys or Data check boxes.

    4. Click Find Next.

    5. Allow the search to run until it finds an entry similar to the following:

      ImagePath = "%Windir%\<the Trojan file name>"

      in a registry key similar to the following:

      HKEY_LOCAL_MACHINE\System\<key name>\Services\<any service name>

    6. If you find such a key, delete it. For example, if you find an entry similar to:

      ImagePath = "C:\WINNT\wxyabc.exe"

      in the key:


      then delete the entire subkey "xabc."

  13. Exit the Registry Editor.

  14. Repeat steps c through e to change back to regedit.exe.

5. To scan for and delete files detected as Backdoor.Exdis
  1. On your Desktop, double-click My Computer.
  2. Right-click your C:\ drive and select one of the following:
    • For Norton AntiVirus consumer products: "Scan with Norton Antivirus"
    • For Symantec AntiVirus Enterprise products: "Scan for Viruses..."
  3. If any files are detected as infected with Backdoor.Exdis, click Delete.

Writeup By: Heather Shannon