Threat description


Category: Malware
Type: Rootkit
Platform: W32
Aliases: Rootkit:W32/Whistler, Rootkit.MBR.Whistler.A, Rootkit.MBR.Whistler.B, rootkit.mbr.whistler.a (boot image), Rootkit.mbr.whistler.b_(boot_image)


Rootkit:W32/Whistler infects the computer system's Master Boot Record (MBR) and loads additional malicious files while the system is starting up (booting).


Automatic action

Once detected, the F-Secure security product may either automatically disinfect the suspect file or prompt the user to select a desired action. For more information, see: Support Community article: Automatic actions for viruses also used for suspicious items.

More scanning & removal options

More information on scanning and removal options available in your F-Secure product can be found in the Help Center.

You may also refer to the Knowledge Base on the F-Secure Community site for further assistance.

Sending a sample to F-Secure Labs

As hidden items are often related to malware, we ask that you consider sending us a sample of the hidden files to F-Secure Labs via the Submit A Sample (SAS) page for further analysis.

Since the files are hidden, you might not be able to access them directly. To access the files, you might need to do one of the following:

  • Start your computer in safe mode. In safe mode, the files may become visible. To do so, you may need to refer to the relevant Microsoft documentation for your specific operating system version.
  • Rename the files. After renaming the files and restarting the computer, the files may become visible. In some cases, the computer must be started in safe mode after renaming for it to be successful.
  • Reboot your system using Windows Recovery Console. The files should be accessible when using the Recovery Console.

Alternatively, if the hidden files are related to the Master Boot Record (MBR), you may use the following instructions:

Manual repair of the Master Boot Record (MBR)

Caution: Manual disinfection of the MBR is only advisable for advanced users.

Microsoft provides tools to replace an infected MBR with a copy of the original, clean MBR. To do so:

  • Boot into the Recovery Console.
  • Depending on the operating system in question, run the appropriate command on all infected drives:
    • On Windows XP, run:fixmbr
    • On Windows 7, run:bootrec

Note: For further information on use of the 'fixmbr' command, please refer to the relevant Microsoft documentation.

Technical Details

F-Secure products may detect the rootkit file itself using the detection names Rootkit.MBR.Whistler.A (boot image) or Rootkit.MBR.Whistler.B (boot image).

As with most rootkits, Whistler is used to help other malicious programs to silently launch themselves on an infected computer. The additional files loaded by the rootkit are stored in the raw disk sectors and are therefore not visible in the file system. These files, which are typically malware, may also be identified by detections such as Gen:Variant.Unruy.4.


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