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Discovered: March 08, 2004
Updated: March 08, 2004 2:28:24 PM
Infection Length: 22,016 bytes
Systems Affected: Windows

W32.Netsky.I@mm is a mass-mailing worm that uses its own SMTP engine to send itself to the email addresses it finds when scanning hard drives and mapped drives.

The Subject, Body, and Attachment vary.


  • Rapid Release definitions version 60307b (extended version 3/7/2004 rev. 2) or higher will detect this threat.
  • The worm has an MD5 hash value of 0xB0E2280F6E952C46D47E563A7C219148.
  • The worm is packed by PE-Pack.
  • Misleading Applications, also known as Rogue Security Software, are fake antivirus programs that display fake virus infection alerts in order to trick users into downloading or paying for the application. Two commonly reported fake infections are “Worm.Win32.Netsky” and “Win32.Netsky.Q”.

    While similar to the name of the threat in this writeup, these fake detections are not related, and running the removal tool will report that no instances of the threat were found on your computer. For more information about Misleading Applications, see the recent Symantec Report on Rogue Security Software.

Antivirus Protection Dates

  • Initial Rapid Release version March 08, 2004
  • Latest Rapid Release version August 08, 2016 revision 023
  • Initial Daily Certified version March 08, 2004
  • Latest Daily Certified version August 09, 2016 revision 001
  • Initial Weekly Certified release date March 08, 2004

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

Technical Description

When W32.Netsky.I@mm is executed, it performs the following actions:

  1. Creates a mutex named "KO[SkyNet.cz]SystemsMutex." This mutex allows only one instance of the worm to execute.

  2. Copies itself as %Windir%\fooding.exe.

    Note: %Windir% is a variable. The W32.Netsky.I@mm locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt) and copies itself to that location.

  3. Adds the value:

    "Tiny AV"="%Windir%\fooding.exe -antivirus service"

    to the registry key:


    so that the worm runs when you start Windows.

  4. Deletes the values:

    • Taskmon
    • Explorer
    • Windows Services Host

      from the registry keys:

    • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

      Note: Some of these registry key values are typically associated with the worms W32.Mydoom.A@mm and W32.Mydoom.B@mm.

  5. Deletes the values:

    • System.
    • msgsvr32
    • service
    • Sentry

      from the registry key:


  6. Deletes the values:

    • d3dupdate.exe
    • au.exe
    • OLE
    • gouday.exe
    • rate.exe
    • sysmon.exe
    • srate.exe
    • ssate.exe
    • sate.exe

      from the registry key:


  7. Deletes the registry keys:

    • HKEY_CLASSES_ROOT\CLSID\{E6FB5E20-DE35-11CF-9C87-00AA005127ED}\InProcServer32
    • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\PINF
    • HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\WksPatch

      Note: The worms W32.Mydoom.A@mm and W32.Mydoom.B@mm add a value to the first key, so that explorer.exe loads their backdoor components.

  8. Scans the following file types on drives C through Z for email addresses:

    • .dhtm
    • .cgi
    • .shtm
    • .msg
    • .oft
    • .sht
    • .dbx
    • .tbb
    • .adb
    • .doc
    • .wab
    • .asp
    • .uin
    • .rtf
    • .vbs
    • .html
    • .htm
    • .pl
    • .php
    • .txt
    • .eml

      Note: Due to a bug in the code, the worm will search a file for email addresses if the extension is a sub-string of one of the aforementioned extensions.

      For example, the worm will scan the files with the .txt, .tx, and .t extensions.

  9. Uses its own SMTP engine to send itself to the email addresses it found above, sending to each address once. The worm uses the local DNS server (retrieved via an API), if available, to perform an MX lookup for the recipient address. If the local DNS fails, it will perform the lookup from the following list of hard-coded servers:


  10. The email has the following characteristics:

    From: service@yahoo.com

    Subject: (One of the following)

    • Mail account expired
    • Mail account closed
    • Mail account deactivated

    Body: (One of the following)

    • Your mail account expired. Please follow the link to reactivate.
    • Your mail account has been closed. Click on the link for further details.
    • Your mail account has been deactivated. To reactivate, follow the link.


    http:/ /www.[recipient domain]/[user]/index.scr

    [recipient domain] and [user] are variable and are taken from the recipient's address. For example, a message to joe@hotmail.com would have the attachment name http:/ /www.hotmail.com/joe/index.scr.

  11. Avoids sending to email addresses that contain any of the following strings:

    • iruslis
    • antivir
    • sophos
    • freeav
    • andasoftwa
    • skynet
    • messagelabs
    • abuse
    • fbi
    • orton
    • f-pro
    • aspersky
    • cafee
    • orman
    • itdefender
    • f-secur
    • avp
    • spam
    • ymantec
    • antivi
    • icrosoft


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. Run a full system scan.
  4. Delete any values added to the registry.

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

1. To disable 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, reenable 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. To update 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.

    If you use Norton AntiVirus 2006, Symantec AntiVirus Corporate Edition 10.0, or newer products, LiveUpdate definitions are updated daily. These products include newer technology.

    If you use Norton AntiVirus 2005, Symantec AntiVirus Corporate Edition 9.0, or earlier products, LiveUpdate definitions are updated weekly. The exception is major outbreaks, when definitions are updated more often.

  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. You should download the definitions from the Symantec Security Response Web site and manually install them.

The latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions . For detailed instructions read the document: How to update virus definition files using the Intelligent Updater .

3. To run a full system scan
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.

    For Norton AntiVirus consumer products: Read the document: How to configure Norton AntiVirus to scan all files.

    For Symantec AntiVirus Enterprise products: Read the document: How to verify that a Symantec Corporate antivirus product is set to scan all files.

  2. Run a full system scan.
  3. If any files are detected, follow the instructions displayed by your antivirus program.
Important: If you are unable to start your Symantec antivirus product or the product reports that it cannot delete a detected file, you may need to stop the risk from running in order to remove it. To do this, run the scan in Safe mode. For instructions, read the document, How to start the computer in Safe Mode . Once you have restarted in Safe mode, run the scan again.
After the files are deleted, restart the computer in Normal mode and proceed with the next section.

Warning messages may be displayed when the computer is restarted, since the threat may not be fully removed at this point. You can ignore these messages and click OK. These messages will not appear when the computer is restarted after the removal instructions have been fully completed. The messages displayed may be similar to the following:

Title: [FILE PATH]
Message body: Windows cannot find [FILE NAME]. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.

4. To delete the value from the registry
Important: 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 subkeys only. For instructions refer to the document: How to make a backup of the Windows registry .
  1. Click Start > Run.
  2. Type regedit
  3. Click OK.

    Note: If the registry editor fails to open the threat may have modified the registry to prevent access to the registry editor. Security Response has developed a tool to resolve this problem. Download and run this tool, and then continue with the removal.

  4. Navigate to and delete the following registry entries:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"Tiny AV"="%Windir%\fooding.exe -antivirus service"

  5. Exit the Registry Editor.

    Note: If the risk creates or modifies registry subkeys or entries under HKEY_CURRENT_USER, it is possible that it created them for every user on the compromised computer. To ensure that all registry subkeys or entries are removed or restored, log on using each user account and check for any HKEY_CURRENT_USER items listed above.

Writeup By: Hiroshi Shinotsuka