Discovered: January 26, 2004
Updated: February 13, 2007 12:16:57 PM
Also Known As: W32.Novarg.A@mm, W32/Mydoom@MM [McAfee], WORM_MIMAIL.R [Trend], Win32.Mydoom.A [Computer Assoc, W32/Mydoom-A [Sophos], I-Worm.Novarg [Kaspersky]
Type: Worm
Systems Affected: Windows

Due to a decreased rate of submissions, Symantec Security Response has downgraded this threat from a Category 3 to a Category 2 rating as of March 30, 2004.

W32.Mydoom.A@mm (also known as W32.Novarg.A) is a mass-mailing worm that arrives as an attachment with the file extension .bat, .cmd, .exe, .pif, .scr, or .zip.

When a computer is infected, the worm sets up a backdoor into the system by opening TCP ports 3127 through 3198, which can potentially allow an attacker to connect to the computer and use it as a proxy to gain access to its network resources.

In addition, the backdoor can download and execute arbitrary files.

There is a 25% chance that a computer infected by the worm will perform a Denial of Service (DoS) on February 1, 2004 starting at 16:09:18 UTC, which is also the same as 08:09:18 PST, based on the machine's local system date/time. If the worm does start the DoS attack, it will not mass mail itself. It also has a trigger date to stop spreading/DoS-attacking on February 12, 2004. While the worm will stop on February 12, 2004, the backdoor component will continue to function after this date.

  • Symantec Consumer products that support Worm Blocking functionality automatically detect this threat as it attempts to spread.
  • Virus definitions dated prior to February 4, 2004 will detect this threat as W32.Novarg.A@mm.

When W32.Mydoom.A@mm sends email, it avoids distributing to the domains that contain any of the following strings:
  • avp
  • syma
  • icrosof
  • msn.
  • hotmail
  • panda
  • sopho
  • borlan
  • inpris
  • example
  • mydomai
  • nodomai
  • ruslis
  • .gov
  • gov.
  • .mil
  • foo.
  • berkeley
  • unix
  • math
  • bsd
  • mit.e
  • gnu
  • fsf.
  • google
  • kernel
  • linux
  • fido
  • usenet
  • iana
  • ietf
  • rfc-ed
  • sendmail
  • arin.
  • ripe.
  • isi.e
  • isc.o
  • secur
  • acketst
  • pgp
  • tanford.e
  • utgers.ed
  • mozilla

    accounts that match any of the following strings:
  • root
  • info
  • samples
  • postmaster
  • webmaster
  • noone
  • nobody
  • nothing
  • anyone
  • someone
  • your
  • you
  • me
  • bugs
  • rating
  • site
  • contact
  • soft
  • no
  • somebody
  • privacy
  • service
  • help
  • not
  • submit
  • feste
  • ca
  • gold-certs
  • the.bat
  • page

    or accounts that contain any of the following strings:
  • admin
  • icrosoft
  • support
  • ntivi
  • unix
  • bsd
  • linux
  • listserv
  • certific
  • google
  • accoun

The worm also prepends any of the following names to the domain name obtained:
  • adam
  • alex
  • alice
  • andrew
  • anna
  • bill
  • bob
  • brenda
  • brent
  • brian
  • claudia
  • dan
  • dave
  • david
  • debby
  • fred
  • george
  • helen
  • jack
  • james
  • jane
  • jerry
  • jim
  • jimmy
  • joe
  • john
  • jose
  • julie
  • kevin
  • leo
  • linda
  • maria
  • mary
  • matt
  • michael
  • mike
  • peter
  • ray
  • robert
  • sam
  • sandra
  • serg
  • smith
  • stan
  • steve
  • ted
  • tom

Antivirus Protection Dates

  • Initial Rapid Release version January 26, 2004
  • Latest Rapid Release version November 04, 2019 revision 019
  • Initial Daily Certified version January 26, 2004
  • Latest Daily Certified version November 04, 2019 revision 065
  • Initial Weekly Certified release date January 26, 2004

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

Technical Description

When W32.Mydoom.A@mm is executed, it does the following:

  1. Creates the following files:
    • %System%\Shimgapi.dll: Shimgapi.dll acts as a proxy server, opening TCP listening ports in the range of 3127 to 3198. The backdoor also has the ability to download and execute arbitrary files.
    • %Temp%\Message: This file contains random letters and is displayed using Notepad.
    • %System%\Taskmon.exe.

    • Taskmon.exe is a legitimate file in the Windows 95/98/Me operating systems, but is in the %Windir% folder, not the %System% folder. (By default, this is C:\Windows or C:\Winnt.) Do not delete the legitimate file in the %Windir% folder.
    • %System% is a variable: The worm locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).
    • %Temp% is a variable: The worm locates the temporary folder and copies itself to that location. By default, this is C:\Windows\TEMP (Windows 95/98/Me), or C:\WINNT\Temp (Windows NT/2000), or C:\Document and Settings\<UserName>\Local Settings\Temp (Windows XP).

  2. Adds the value:

    "(Default)" = "%System%\shimgapi.dll"

    to the registry key:


    so that Explorer.exe loads Shimgapi.dll.

  3. Adds the value:

    "TaskMon" = "%System%\taskmon.exe"

    to the registry keys:



    so that TaskMon is run when you start Windows.

  4. Checks the system date, and if the date is between February 1, 2004 and February 12, 2004, there is a 25% chance the worm will perform a DoS attack against The DoS is performed by creating 63 new threads that send GET requests and use a direct connection to port 80. The worm will not mass mail itself if the DoS attack is triggered.

    • The DoS attack will start at 16:09:18 UTC (08:09:18 PST) on February 1, 2004. The worm checks the local system time and date to determine if it should initiate the DoS attack.
    • Due to the way the worm verifies the system date, the DoS will only be executed on 25% of infected computers.
    • The DoS will only occur when the system date is checked during the initial infection, or if the computer is restarted.
    • The worm will use local DNS settings to resolve the domain name used in the DoS attack (

  5. Creates the following registry keys:



  6. Searches for the email addresses in the files with the following extensions:
    • .htm
    • .sht
    • .php
    • .asp
    • .dbx
    • .tbb
    • .adb
    • .pl
    • .wab
    • .txt

  7. Attempts to send email messages using its own SMTP engine. The worm looks up the mail server that the recipient uses before sending the email. If it is unsuccessful, it will use the local mail server instead. The email will have the following characteristics:

    From: The "From" address may be spoofed.

    Subject: The subject will be one of the following:
    Mail Delivery System
    Mail Transaction Failed
    Server Report

    Message: The message will be one of the following:
    Mail transaction failed. Partial message is available.
    The message contains Unicode characters and has been sent as a binary attachment.
    The message cannot be represented in 7-bit ASCII encoding and has been sent as a binary attachment.

    Attachment: The attachment file name, not including the extension, will be one of the following:

    The attached file may have either one or two file extensions. If it does have two, the first extension will be one of the following:

    The second extension, or the only extension if there is only one, will be one of the following:
    .zip (This is an actual .zip file that contains a copy of the worm, sharing the same file name as the .zip. For example, can contain readme.exe.)

    If the worm has an extension of .exe or .scr, the file will be displayed with the following icon:

    For all the other file extensions, it will use the icon for that file type.

  8. Copies itself to the Kazaa download folder as one of the following files:
    • winamp5
    • icq2004-final
    • activation_crack
    • strip-girl-2.0bdcom_patches
    • rootkitXP
    • office_crack
    • nuke2004

      with a file extension of:
    • .pif
    • .scr
    • .bat
    • .exe

Symantec Client Security
  • Antivirus component: An update for the Symantec Client Security AntiVirus engine to protect against the W32.Mydoom.A@mm/W32.Novarg.A@mm worm has been available for several days via LiveUpdate (see above).
  • Symantec Client Firewall: Symantec Client Firewall ships with the default ruleset as "High: Block everything until you allow it." It will notify the user of the exploit backdoor connection and prompt the user to Permit, Block, or Customize a rule for that connection attempt opened by the virus MyDoom/Novarg.

Symantec Gateway Security 1.0
An update for the Symantec Gateway Security IDS/IPS engine to protect against the W32.Mydoom.A@mm worm has been posted as of 9:24 PM PST 1/30/04. Symantec Gateway Security administrators are advised to run LiveUpdate to ensure protection against this threat.

Symantec Gateway Security 2.0
An update for the Symantec Gateway Security IDS/IPS engine to protect against the W32.Mydoom.A@mm worm has been posted as of 3:02 PM PST 1/29/04. Symantec Gateway Security administrators are advised to run LiveUpdate to ensure protection against this threat.

Intruder Alert
Symantec has released the Intruder Alert 3.6 W32_Novarg_Worm Policy .

Symantec HIDS 4.1.1
Symantec released a LiveUpdate package on January 27, 2004 for users of Symantec HIDS 4.1.1. See the Symantec Host IDS 4.1.1 Security Update 1 for additional information.

Symantec ManHunt
Security Update 17 has been released to provide signatures specific to the backdoor activity associated with the W32.Mydoom.A@mm Worm.

DoS detection via ManHunt Flow Alert Rules: The Symantec Network IDS team recommends that administrators use the Flow Alert Rule feature to log events for suspicious traffic to the SCO Web site on 2/1/2004 and the Microsoft Web site on 2/3/2004. For detailed instructions, read the Symantec Knowledge Base at:

In addition, Symantec ManHunt 2.2/3.0/3.01 customers can apply the following signature to detect the attempted DoS against This DoS will start occurring on February 1, 2004. On February 12, 2004 the worm has a trigger date to stop spreading. This signature will help in determining from which machines the request is being made.

*******************start file********************

alert tcp any any -> any 80 (msg:"W32_Novarg_SCO_DOS"; content:"GET / HTTP/1.1|0d0a|Host:|0d0a0d0a|"; offset:0; dsize:37;)


For more information on creating custom signatures, refer to the "Symantec ManHunt Administrative Guide: Appendix A Custom Signatures for HYBRID Mode."


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.


Removal using the Removal Tool
Symantec Security Response has developed a removal tool to clean the infections of W32.Mydoom.A@mm. This is the preferred method in most cases.

Manual Removal
Perform a manual removal if you cannot obtain the tool.

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.Mydoom.A@mm.
  5. Delete the values that were added to the registry.
  6. Reregister the webcheck.dll file. (This will remove the registry modifications responsible for loading Shimgapi.dll.)
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.Mydoom.A@mm, click Delete.

5. Deleting the values 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 each of these keys:



  4. In the right pane, delete the value:


    Note: %System% is a variable that refers to the location of the System folder. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

  5. Exit the Registry Editor.

6. Reregistering the Webcheck.dll file
(This will remove the registry modifications responsible for loading Shimgapi.dll.)
  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type, or copy and paste, the following text:

    regsvr32 webcheck.dll

  3. Click OK. When you see the message, "DllRegisterServer in webcheck.dll
    succeeded," click OK.

Writeup By: Peter Ferrie