Printer Friendly Page

Discovered: March 17, 2004
Updated: February 13, 2007 12:19:12 PM
Also Known As: W32/Netsky.o@MM [McAfee], WORM_NETSKY.O [Trend]
Type: Worm
Systems Affected: Windows

W32.Netsky.O@mm is a mass-mailing worm that uses its own SMTP engine to send itself to the email addresses it finds when scanning the hard drives and mapped drives. The "sender" of the email is spoofed, and its subject line and message body of the email vary.

The attachment is one of the following:

    • readme.pif
    • document.pif
    • data.pif
    • details.pif
    • msg.pif
    • message.pif

This threat is compressed with UPX.

  • Symantec Consumer products that support Worm Blocking functionality automatically detect this threat as it attempts to spread.
  • The worm executable has a static MD5 hash value of 0x9D7006E30FDF15E9C8E03E62534B3A3E

Antivirus Protection Dates

  • Initial Rapid Release version March 17, 2004
  • Latest Rapid Release version September 12, 2017 revision 020
  • Initial Daily Certified version March 17, 2004
  • Latest Daily Certified version September 13, 2017 revision 002
  • Initial Weekly Certified release date March 17, 2004

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

Writeup By: Yana Liu

Discovered: March 17, 2004
Updated: February 13, 2007 12:19:12 PM
Also Known As: W32/Netsky.o@MM [McAfee], WORM_NETSKY.O [Trend]
Type: Worm
Systems Affected: Windows

When W32.Netsky.O@mm runs, it does the following:

  1. Creates a mutex to allow only one instance of the worm to execute.

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

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

  3. Creates the file, %Windir%\base64.bmp (22,456 bytes), which is a MIME64_encoded worm.

  4. Adds the value:


    to the registry key:


    so that the worm runs when you start Windows.

  5. Deletes these values:

    Windows Services Host

    from the registry key:


  6. Deletes the value: system.

    from the registry key:


  7. Deletes these values:

    Windows Services Host

    from the registry key:


  8. Deletes the value:


    from the registry key:


  9. Deletes the following subkeys:


  10. Retrieves email addresses from the files with these extensions on drives C to Z :
    • .adb
    • .asp
    • .cgi
    • .dbx
    • .dhtm
    • .doc
    • .eml
    • .htm
    • .html
    • .jsp
    • .msg
    • .oft
    • .php
    • .pl
    • .rtf
    • .sht
    • .shtm
    • .tbb
    • .txt
    • .uin
    • .vbs
    • .wab
    • .wsh
    • .xml

  11. Uses its own SMTP engine to send itself to the email addresses it finds.

    The email has the following characteristics:

    From: <Spoofed>

    Subject: The subject line is one of the following:
    • Re: Encrypted Mail
    • Re: Extended Mail
    • Re: Status
    • Re: Notify
    • Re: SMTP Server
    • Re: Mail Server
    • Re: Delivery Server
    • Re: Bad Request
    • Re: Failure
    • Re: Thank you for delivery
    • Re: Test
    • Re: Administration
    • Re: Message Error
    • Re: Error
    • Re: Extended Mail System
    • Re: Secure SMTP Message
    • Re: Protected Mail Request
    • Re: Protected Mail System
    • Re: Protected Mail Delivery
    • Re: Secure delivery
    • Re: Delivery Protection
    • Re: Mail Authentification
    Message: The message body is one of the following:
    • Please confirm my request.
    • ESMTP [Secure Mail System #334]: Secure message is attached.
    • Partial message is available.
    • Waiting for a Response. Please read the attachment.
    • First part of the secure mail is available.
    • For more details see the attachment.
    • For further details see the attachment.
    • Your requested mail has been attached.
    • Protected Mail System Test.
    • Secure Mail System Beta Test.
    • Forwarded message is available.
    • Delivered message is attached.
    • Encrypted message is available.
    • Please read the attachment to get the message.
    • Follow the instructions to read the message.
    • Please authenticate the secure message.
    • Protected message is attached.
    • Waiting for authentification.
    • Protected message is available.
    • Bad Gateway: The message has been attached.
    • SMTP: Please confirm the attached message.
    • You got a new message.
    • Now a new message is available.
    • New message is available.
    • You have received an extended message. Please read the instructions.

      Followed by one of the following:
    • +++ Attachment: No Virus found
      +++ Panda AntiVirus - You are protected
      +++ www.pandasoftware.com
    • +++ Attachment: No Virus found
      +++ Norman AntiVirus - You are protected
      +++ www.norman.com
    • +++ Attachment: No Virus found
      +++ F-Secure AntiVirus - You are protected
      +++ www.f-secure.com
    • +++ Attachment: No Virus found
      +++ Norton AntiVirus - You are protected
      +++ www.symantec.de
    Attachment: The attachment is one of the following:
    • readme.pif
    • document.pif
    • data.pif
    • details.pif
    • msg.pif
    • message.pif


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.

Writeup By: Yana Liu

Discovered: March 17, 2004
Updated: February 13, 2007 12:19:12 PM
Also Known As: W32/Netsky.o@MM [McAfee], WORM_NETSKY.O [Trend]
Type: Worm
Systems Affected: Windows

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. Restart the computer in Safe Mode, or end the worm process.
  4. Run a full system scan and delete all the files detected as W32.Netsky.O@mm.
  5. Delete the value that was added to the registry.
For specific details on each of these steps, read the following instructions.

1. Disabling 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, re-enable 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. 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.

3. Restarting the computer in Safe mode or VGA Mode
Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode or VGA mode.
  • For Windows 95, 98, Me, 2000, or XP users, restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."
  • For Windows NT 4 users, restart the computer in VGA mode.
4. 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 W32.Netsky.O@mm, click Delete.

5. Deleting the value from the registry

WARNING: 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 the key:


  4. In the right pane, delete the value:


  5. Exit the Registry Editor.

Writeup By: Yana Liu