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Discovered: April 14, 2004
Updated: February 13, 2007 12:21:25 PM
Also Known As: W32/Netsky.v@MM [McAfee], WORM_NETSKY.V [Trend], W32/Netsky-V [Sophos], Win32.Netsky.V [Computer Assoc
Type: Worm
Systems Affected: Windows

W32.Netsky.V@mm is a mass-mailing worm that sends itself to the email addresses that it gathers from the files on the computer. This variant does not send an attachment with its email messages, but instead sends a link to an infected computer, attempting to download and run the worm's executable.

The From line of the email is spoofed, and the Subject line and message body vary.

The worm is packed with UPXSh!t v0.07, UPXSh!t v0.06, and UPX 1.24.

Antivirus Protection Dates

  • Initial Rapid Release version April 15, 2004
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version April 15, 2004
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date April 17, 2004

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

Technical Description

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

  1. Copies itself using the following file names:
    • %Windir%\Kasperskyaveng.exe
    • %Windir%\skyav.tmp

      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.

  2. Creates a mutex named "_-=oOOSOkOyONOeOtOo=-_", which allows only one instance of the worm to execute.

  3. Adds the value:


    to the registry key:


    so that the worm runs when you start Windows.

  4. Enumerates all the hard drives and retrieves the email addresses from files with the following extensions:
    • .a
    • .ad
    • .adb
    • .as
    • .asp
    • .c
    • .cf
    • .cfg
    • .cg
    • .cgi
    • .d
    • .db
    • .dbx
    • .dh
    • .dht
    • .dhtm
    • .do
    • .doc
    • .e
    • .em
    • .eml
    • .h
    • .ht
    • .htm
    • .html
    • .j
    • .js
    • .jsp
    • .m
    • .mb
    • .mbx
    • .md
    • .mdx
    • .mh
    • .mht
    • .mm
    • .mmf
    • .ms
    • .msg
    • .n
    • .nc
    • .nch
    • .o
    • .od
    • .ods
    • .of
    • .oft
    • .p
    • .ph
    • .php
    • .pl
    • .pp
    • .ppt
    • .r
    • .rt
    • .rtf
    • .s
    • .sh
    • .sht
    • .shtm
    • .st
    • .stm
    • .t
    • .tb
    • .tbb
    • .tx
    • .txt
    • .u
    • .ui
    • .uin
    • .v
    • .vb
    • .vbs
    • .w
    • .wa
    • .wab
    • .ws
    • .wsh
    • .x
    • .xl
    • .xls
    • .xm
    • .xml

  5. If the computer's system date is between April 22, 2004 and April 29, 2004, it will attempt to perform a Denial of Service (DoS) attack against the following Web sites:
    • www.keygen.us
    • www.freemule.net
    • www.kazaa.com
    • www.emule.de
    • www.cracks.am

  6. Installs an HTTP server that listens on TCP port 5557.

  7. Installs an FTP server that listens on TCP port 5556. The FTP connection is logged in the file, c:\fvw.log.

  8. Uses its own SMTP client engine to send itself to the email addresses that it finds.

    The email has the following characteristics:

    From: (May be spoofed using the following email address)

    Subject: (One of the following)
    • Gateway Status failure
    • Server Status failure
    • Mail delivery failed
    • Mail Delivery Sytem failure

      Body: (One of the following)
    • The processing of this message can take a few minutes...
    • Converting message. Please wait...
    • Please wait while loading failed message...
    • Please wait while converting the message...

Replication Process
The replication is provided using the mechanism of known vulnerabilities, as shown in the diagram below:

  1. W32.Netsky.V@mm constructs a message body using the Microsoft Internet Explorer XML Page Object Type Validation vulnerability (described in Microsoft Security Bulletin MS03-040). This vulnerability could allow a malicious object to be trusted, installed, and then executed on the targeted computer.

    The email body contains the object that points to the following source:

    http:/ /%infected_computer_ip%:5557/index.html

    where %infected_computer_ip% is the IP address of the infected computer.

  2. The targeted computer requests the index.html page on the infected computer, accessing the HTTP server listening on port 5557.

  3. The HTTP server creates an index.html page that exploits the Microsoft IE5 ActiveX "Object for constructing type libraries for scriptlets" vulnerability (described in Microsoft Security Bulletin MS99-032).

  4. The viral index.html file launches ftp.exe, which is the default FTP client in Windows.

    Ftp.exe connects to the FTP server listening on port 5556 on the infected computer, and then requests the worm executable.

  5. The worm executable is sent to the targeted computer, and then executed.


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.


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 VGA mode.
  4. Run a full system scan and delete all the files detected as W32.Netsky.V@mm.
  5. Reverse the changes made to the registry.

For 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, 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. 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: 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. To restart 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. To scan for and delete 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.V@mm, click Delete.

5. To reverse the changes made to 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.

  6. Restart the computer in Normal mode. For instructions, read the section on returning to Normal mode in the document, "How to start the computer in Safe Mode."

Writeup By: Sergei Shevchenko