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 security response

Backdoor.Agent.B Removal Tool

Discovered on: August 10, 2004
Last Updated on: August 24, 2004 03:58:14 PM PDT

Symantec Security Response has developed a removal tool to clean the following infections:

Backdoor.Agent.B

Please download the tool from: http://securityresponse.symantec.com/avcenter/FxAgentB.exe


Important:

  • If you are on a network or have a full-time connection to the Internet, such as a DSL or cable modem, disconnect the computer from the network and Internet. Disable or password-protect file sharing, or set the shared files to Read Only, before reconnecting the computers to the network or to the Internet. Because this worm spreads by using shared folders on networked computers, to ensure that the worm does not re-infect the computer after it has been removed, Symantec suggests sharing with Read Only access or by using password protection.

    For instructions on how to do this, refer to your Windows documentation, or the document, "How to configure shared Windows folders for maximum network protection."
  • If you are removing an infection from a network, first make sure that all the shares are disabled or set to Read Only.
  • This tool is not designed to run on Novell NetWare servers. To remove this threat from a NetWare server, first make sure that you have the current virus definitions, and then run a full system scan with the Symantec antivirus product.


How to download and run the tool

Important: You must have administrative rights to run this tool on Windows NT 4.0, Windows 2000, or Windows XP.

Note for network administrators: If you are running MS Exchange 2000 Server, we recommend that you exclude the M drive from the scan by running the tool from a command line, with the Exclude switch. For more information, read the Microsoft knowledge base article, "XADM: Do Not Back Up or Scan Exchange 2000 Drive M" (Article 298924).

Follow these steps to download and run the tool:
  1. Download the FxAgentB.exe file from: http://securityresponse.symantec.com/avcenter/FxAgentB.exe
  2. Save the file to a convenient location, such as your Windows desktop.
  3. Optional: To check the authenticity of the digital signature, refer to the "Digital signature" section later in this writeup.

    Note:     If you are sure that you are downloading this tool from the Security Response Web site, you can skip this step. If you are not sure, or are a network administrator and need to authenticate the files before deployment, follow the steps in the "Digital signature" section before proceeding with step 4.
  4. Close all the running programs.
  5. If you are on a network or if you have a full-time connection to the Internet, disconnect the computer from the network and the Internet.
  6. If you are running Windows Me or XP, turn off System Restore. For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
  7. Locate the file that you just downloaded.
  8. Double-click the FxAgentB.exe file to start the removal tool.
  9. When the following message appears, click OK:

    Please do NOT start any other applications until the removal tool exits and the computer is restarted.

    Doing so may cause reinfection.
  10. Click Start to begin the process, and then allow the tool to run.
  11. Restart the computer.
  12. Run the removal tool again to ensure that the system is clean.
  13. If you are running Windows Me/XP, then re-enable System Restore.
  14. If you are on a network or if you have a full-time connection to the Internet, reconnect the computer to the network or to the Internet connection.
  15. Run LiveUpdate to make sure that you are using the most current virus definitions.

When the tool has finished running, you will see a message indicating whether Backdoor.Agent.B has infected the computer. The tool displays results similar to the following:
  • Total number of the scanned files
  • Number of deleted files
  • Number of repaired files
  • Number of terminated viral processes
  • Number of terminated viral threads
  • Number of fixed registry entries

What the tool does

The Backdoor.Agent.B Removal Tool does the following:
  1. Terminates the Backdoor.Agent.B threads
  2. Deletes the Backdoor.Agent.B files
  3. Deletes the registry values that the Backdoor.Agent.B added


Switches:

The following switches are designed for use by network administrators:

Switch
Description

/HELP, /H, /?
Displays the help message.

/SILENT, /S
Enables the silent mode.

/LOG=<path name>
Creates a log file where <path name> is the location in which to store the tool's output. By default, this switch creates the log file, FxAgentB.log, in the same folder from which the removal tool was executed.

/START
Forces the tool to immediately start scanning.

/EXCLUDE=<path>
Excludes the specified <path> from scanning. (We do not recommend using this switch. See the following Note.)

The /EXCLUDE switch will only work with one path, not multiple. The following is an example command line that can be used to exclude a single drive:

"C:\Documents and Settings\user1\Desktop\FxAgentB.exe" /EXCLUDE=M:\ /LOG=c:\FxAgentB.txt

Note: You can give the log file any name and save it to any location.



Digital signature
For security purposes, FxAgentB.exe is digitally signed. Symantec recommends that you use only copies of FxAgentB.exe that have been directly downloaded from the Symantec Security Response Web site.

If you are not sure, or are a network administrator and need to authenticate files before deployment, you should check the authenticity of the digital signature.

Follow these steps:
  1. Go to http://www.wmsoftware.com/free.htm.
  2. Download and save the Chktrust.exe file to the same folder in which you saved FxAgentB.exe.

    Note:     Most of the following steps are done at a command prompt. If you downloaded the removal tool to the Windows desktop, it will be easier if you first move the tool to the root of the C drive. Then save the Chktrust.exe file to the root of C as well.

    (Step 3 to assume that both the removal tool and Chktrust.exe are in the root of the C drive.)
  3. Click Start > Run.
  4. Type one of the following:
    • Windows 95/98/Me:

      command
    • Windows NT/2000/XP:

      cmd
  5. Click OK.
  6. In the command window, type the following, pressing Enter after typing each line:

    cd\
    cd downloads
    chktrust -i FxAgentB.exe

    You should see the message:

    "Do you want to install and run "Backdoor.Agent.B Removal Tool" signed on 08/19/2004 2:26pm and distributed by Symantec Corporation?"

    Notes:
    • The date and time displayed in this dialog box will be adjusted to your time zone, if your computer is not set to the Pacific time zone.
    • If you are using Daylight Saving time, the displayed time will be exactly one hour earlier.
    • If this dialog box does not appear, there are two possible reasons:
      • The tool is not from Symantec: Unless you are sure that the tool is legitimate and that you downloaded it from the legitimate Symantec Web site, you should not run it.
      • The tool is from Symantec and is legitimate: However, your operating system was previously instructed to always trust content from Symantec. For information on this and on how to view the confirmation dialog again, read the document, "How to restore the Publisher Authenticity confirmation dialog box."

  7. Click Yes to close the dialog box.
  8. Type exit, and then press Enter. (This will close the MS-DOS session.)


Write-up by: Sergei Shevchenko and Robert X Wang