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Discovered: April 02, 2003
Updated: February 13, 2007 11:45:10 AM
Also Known As: Backdoor.GrayBird [KAV], BackDoor-ARR [McAfee]
Type: Trojan Horse
Systems Affected: Windows

Backdoor.Graybird is a back door Trojan Horse that gives its creator unauthorized access to your computer. The existence of the file, Svch0st.exe, is an indication of a possible infection. Backdoor.Graybird is a Delphi application.

Antivirus Protection Dates

  • Initial Rapid Release version April 02, 2003
  • Latest Rapid Release version January 15, 2020 revision 019
  • Initial Daily Certified version April 02, 2003 revision 007
  • Latest Daily Certified version January 13, 2020 revision 003
  • Initial Weekly Certified release date April 02, 2003

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

Technical Description

When Backdoor.Graybird runs, it performs the following actions:

  1. Copies itself as one of the following filenames:
    • %System%\Svch0st.exe
    • %System%\Winlogon.exe
    • %System%\Explorer.exe
    • %System%\ravmond.exe

      %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).

  2. Creates one of the following values, or a similar value, depending on the variant:

    "svchost" = "%System%\Svch0st.exe"
    "winlogon" = "%System%\Winlogon.exe"
    "system" = "%System%\Explorer.exe"
    "ravmond" = "%System%\Explorer.exe"

    in the registry keys:


    so that the Trojan runs when you start Windows.

  3. If the operating system is Windows NT/2000/XP, the Trojan also creates the value:

    "run" = "%system%\svch0st.EXE"
    "run" = "%system%\ravmond.exe"

    in the registry key:

    HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows

  4. If the operating system is Windows 95/98/Me, the Trojan adds the line to the [windows] section of the Win.ini file:


    so that the Trojan runs when you start Windows.

  5. Attempts to access the password cache stored on your computer. The cached passwords include, amongst others, the modem and dialup passwords, URL passwords, and share passwords.

  6. Intercepts keystrokes allowing Backdoor.Graybird to steal confidential information.

  7. Once Backdoor.Graybird is installed, it waits for the commands from the remote client.

    These commands allow the Trojan's creator to perform any of the following actions:
    • Deliver system and network information to the Trojan's creator, including the login names and cached network passwords.
    • Install an FTP server, allowing the hacker to use the compromised computer as a temporary storage device.
    • Open or close the CD-ROM drive and perform other annoying actions.
    • Download and execute files.


    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.


    The following 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. Do one of the following:
      • Windows 95/98/Me: Restart the computer in Safe mode.
      • Windows NT/2000/XP: End the Trojan process.
    3. Run a full system scan and delete all the files detected as Backdoor.Graybird.
    4. Reverse the changes that the Trojan made to the registry.
    5. Reverse the changes that the Trojan made to the Win.ini file (Windows 95/98/Me only).
    For 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 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.

    2. Restarting the computer in Safe mode or ending the Trojan process
      Windows 95/98/Me
      Restart the computer in Safe mode. All the Windows 32-bit operating systems, except for 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."

      Windows NT/2000/XP
      To end the Trojan process:
      1. Press Ctrl+Alt+Delete once.
      2. Click Task Manager.
      3. Click the Processes tab.
      4. Double-click the Image Name column header to alphabetically sort the processes.
      5. Scroll through the list and look for Svch0st.exe.
      6. If you find the file, click it, and then click End Process.
      7. Exit the Task Manager.
    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.Graybird, click Delete.

    4. Reversing the changes made to the registry

    : 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. 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 the keys:


      NOTE: All the keys do not exist on all the systems.

    4. For each one, in the right pane, delete any of the following values:

      "svchost" = "%System%\Svch0st.exe"
      "winlogon" = "%System%\Winlogon.exe"
      "system" = "%System%\Explorer.exe"
      "ravmond" = "%System%\Explorer.exe"

    5. If you are running Windows NT/2000/XP, navigate to the key:

      HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows

    6. In the right pane, delete the value:

      "run" = "%system%\svch0st.EXE"
      "run" = "%system%\ravmond.exe"

    7. Exit the registry editor.

    4. Reversing the changes made to the Win.ini file
    If you are running Windows 95/98/Me, follow these steps:
    1. The function you perform depends on your operating system:
      • Windows 95/98: Go to step b.
      • Windows Me: If you are running Windows Me, the Windows Me file-protection process may have made a backup copy of the Win.ini file that you need to edit. If this backup copy exists, it will be in the C:\Windows\Recent folder. Symantec recommends deleting this file before continuing with the steps in this section. To do this:
        1. Start Windows Explorer.
        2. Browse to and select the C:\Windows\Recent folder.
        3. In the right pane, select the Win.ini file and delete it. The Win.ini file will be regenerated when you save your changes to it in step f.

    2. Click Start, and then click Run.
    3. Type the following:

      edit c:\windows\win.ini

      and then click OK. (The MS-DOS Editor opens.)

      NOTE: If Windows is installed in a different location, make the appropriate path substitution.

    4. In the [windows] section of the file, look for a line similar to:


    5. If this line exists, delete the entire line.

    6. Click File, and then click Save.

    7. Click File, and then click Exit.

    Writeup By: Serghei Sevcenco