Trojan.Zeroaccess Removal Tool

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Discovered: July 13, 2011
Type: Removal Information

This tool is designed to remove the infections of Trojan.Zeroaccess and Trojan.Zeroaccess.B .


  • 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 designed to run on 32-bit and 64-bit computers.

How to download and run the tool

Important: You must have administrative rights to run this tool on Windows XP, Windows Vista, or Windows 7.

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: Issues caused by a back up or a scan of the Exchange 2000 M drive (Article 298924). Follow these steps to download and run the tool:
  1. Download the FixZeroAccess.exe file from: Trojan.Zeroaccess Removal Tool.
  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.

    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 running programs.
  5. If you are running Windows XP, turn off System Restore. For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles: How to turn off or turn on Windows XP System Restore
  6. Locate the file that you just downloaded.
  7. Double-click the FixZeroAccess.exe file to start the removal tool.
  8. Click Start to begin the process, and then allow the tool to run.
  9. Restart the computer when prompted by the tool.
  10. After the computer has started, the tool will inform you of the state of infection.
  11. If you are running Windows XP, re-enable System Restore.
  12. Run LiveUpdate to make sure that you are using the most current virus definitions.
When the tool has finished running (Step 10), you will see a message indicating whether the threat has infected the computer.

What the tool does

The Removal Tool does the following:
  • Terminates the associated processes
  • Deletes the associated files
  • Removes hidden partition unconditionally if detection occurs

Digital signature
For security purposes, the removal tool is digitally signed. Symantec recommends that you use only copies of the removal tool that have been directly downloaded from the Symantec Security Response website. 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
  2. Download and save the Chktrust.exe file to the same folder in which you saved the removal tool.

    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 assumes that both the removal tool and Chktrust.exe are in the root of the C drive.)

  3. Click Start > Run.
  4. Type the following: cmd
  5. Click OK.
  6. In the command window, type the following, pressing Enter after typing each line: cd\ cd downloads chktrust -i FixZeroAccess.exe
  7. You should see one of the following messages, depending on your operating system:

    Windows XP SP2:
    The Trust Validation Utility window will appear. Under Publisher, click the Symantec Corporation link. The Digital Signature Details appears.

    Verify the contents of the following fields to ensure that the tool is authentic:
    Symantec Corporation
    Signing Time:
    12/07/2011 00:05:46

    All other operating systems:
    You should see the following message: Do you want to install and run "FixZeroAccess.exe" signed on Wednesday, December 7, 2011 00:05:46 and distributed by Symantec Corporation?

    The date and time in the digital signature above are based on Pacific time. They will be adjusted for your computer's time zone and Regional Options settings. 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 website, 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.
  8. Click Yes or Run to close the dialog box.
  9. Type exit, and then press Enter. (This will close the MS-DOS session.)

    If the removal tool is unable to repair/replace an infected rootkit driver, a message will be displayed explaining that it will need to be restored manually.

Manually restoring infected drivers

To manually restore an infected driver it is necessary to restart the computer and run the Windows Recovery Console. For full details on how to do this please read the Microsoft Knowledge Base article, How to install and use the Recovery Console in Windows XP .
  1. Insert the Windows XP/Vista/7 CD-ROM into the CD-ROM drive.
  2. Restart the computer from the CD-ROM drive.
  3. XP: Press R to start the Recovery Console when the "Welcome to Setup" screen appears.
    Vista/7: Follow the instructions on the screen and click Next > Repair Your Computer.
  4. Select the installation that you want to access from the Recovery Console.
  5. XP: Enter the administrator password and press Enter.
    Vista/7: If prompted, enter your user name and password.
  6. (Vista/7 users must first select Command Prompt before following this step)
    Type the following commands and press Enter after each command:
    • cd %System% [DLL FILE] or
    • cd %System%\drivers [SYS FILES]
    • expand [CD/DVD DRIVE]:\i386\[DETECTED FILE NAME].[dl or sy]_
    For example:
    • cd c:\windows\system32\drivers
    • expand d:\i386\atapi.sy_
  7. Repeat the above step for each SYS file affected. See the Technical Description section for a list of files that may be affected.
  8. Type exit.
  9. Press Enter. The computer will now restart automatically.