Discovered: February 26, 2005
Updated: February 13, 2007 12:34:14 PM
Also Known As: Win32.Mytob.B [Computer Associ, Mytob.A [F-Secure], Net-Worm.Win32.Mytob.a [Kasper, W32/ [McAfee], W32/Mytob-A [Sophos], WORM_MYTOB.A [Trend Micro]
Type: Worm
Systems Affected: Windows

W32.Mytob.@mm is a mass-mailing worm that uses it own SMTP engine to send an email to addresses that it gathers from the Windows Address Book on the compromised computer. The worm also has the ability to open a back door and spread through the network by exploiting vulnerabilities.

Antivirus Protection Dates

  • Initial Rapid Release version February 26, 2005
  • Latest Rapid Release version July 10, 2019 revision 004
  • Initial Daily Certified version February 26, 2005 revision 002
  • Latest Daily Certified version July 10, 2019 revision 007
  • Initial Weekly Certified release date February 27, 2005

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

Technical Description

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

  1. Copies itself to the %System% folder. Some variants may have the following file name:


    Note: %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).

  2. May create and share a folder on the Kazaa file-sharing network, by adding the following registry value:

    "dir0" = "012345:[CONFIGURABLE PATH]"

    to the registry subkey:


  3. Copies itself to the configured path as file names that are designed to trick other users into downloading and executing the worm.

  4. May perform Denial of Service attacks on specified servers.

  5. May end security application processes.

  6. Connects to specified IRC servers and joins a channel to receive commands. The commands may include the following:

    • Scan for vulnerable computers
    • Download or upload files
    • List or end running processes
    • Steal cached passwords
    • Log keystrokes to steal information entered into windows with titles containing the following strings:

      • bank
      • login
      • e-bay
      • ebay
      • paypal
    • Start a local HTTP, FTP, or TFTP server
    • Search for files on the compromised computer
    • Capture screenshots, data from the clipboard, and footage from webcams
    • Visit URLs
    • Flush the DNS and ARP caches
    • Open a command shell on the compromised computer
    • Intercept packets on the local area network
    • Send net send messages
    • Copy itself to many hard-coded Windows startup folders, such as the following:

      • Documents and Settings\All Users\Menu Start\Programma's\Opstarten
      • WINDOWS\All Users\Start Menu\Programs\StartUp
      • WINNT\Profiles\All Users\Start Menu\Programs\Startup
      • WINDOWS\Start Menu\Programs\Startup
      • Documenti e Impostazioni\All Users\Start Menu\Programs\Startup
      • Dokumente und Einstellungen\All Users\Start Menu\Programs\Startup
      • Documents and Settings\All Users\Start Menu\Programs\Startup

        Note: Symantec Security Response has received reports of variants of this worm creating zero-byte files in the Startup folder. These files may have file names such as TFTP780 or TFTP###, where # can be any number

  7. Adds a variable registry value to one or more of the following registry subkeys:


    For example:

    "MSN" = "msnmsgr.exe"

  8. May create a random subkey with random values under the following subkey:


  9. May create a random subkey under the following subkey:


  10. May modify one of the following values:

    "EnableDCOM" = "Y"
    "EnableDCOM" = "N"

    in the registry subkey:


    which enables or disables DCOM settings, depending on the command from the attacker.

  11. May modify the value:

    "restrictanonymous" = "1"

    in the registry subkey:


    to restrict network access.

  12. May modify the value:

    "Start" = "4"

    in the registry subkey:


    to disable the SharedAccess service in Windows 2000/XP.

  13. May modify the values:

    "AutoShareWks" = "0"
    "AutoShareServer" = "0"

    in the registry subkeys:


  14. May modify the value:

    "DoNotAllowXPSP2" = "1"

    in the registry subkey:


    to prevent Windows XP SP2 from being installed on the compromised computer.

  15. May send confidential information, such as the operating system, IP address, user name, etc., to the IRC server.

  16. May open a back door on a random port.

  17. May register itself as a service.

  18. May drop a device driver file named %System%\haxdrv.sys.

  19. May start proxy server for HTTP, SOCKS4, or SMTP protocol.

  20. May port scan the network.

  21. May attempt to connect to MS SQL servers with weak Administrator or SA passwords, and copy itself to the computer if successful. The following passwords could be applied in an attempt to authenticate to the remote server:

    • null
    • Rendszergazda
    • Beheerder
    • amministratore
    • hallintovirkailijat
    • Administrat
    • Administrateur
    • administrador
    • Administrador
    • administrator
    • Administrator
    • Password
    • password
    • admin
    • 123

  22. May be able to enumerate through accounts on the computer and disable the "SeNetworkLogonRight" Authorization Constant to explicitly deny an account the right to log on using the network log on type.

  23. May attempt to enumerate users in order to copy itself to network shares. The following passwords could be applied in an attempt to authenticate to the remote share:

    • 007
    • 123
    • 1234
    • 12345
    • 123456
    • 1234567
    • 12345678
    • 123456789
    • 1234567890
    • 2000
    • 2001
    • 2002
    • 2003
    • 2004
    • access
    • accounting
    • accounts
    • adm
    • administrador
    • administrat
    • administrateur
    • administrator
    • admins
    • amministratore
    • asd
    • backup
    • beheerder
    • bill
    • bitch
    • blank
    • bob
    • brian
    • changeme
    • chris
    • cisco
    • compaq
    • computer
    • control
    • data
    • database
    • databasepass
    • databasepassword
    • db1
    • db1234
    • db2
    • dba
    • dbpass
    • dbpassword
    • default
    • dell
    • demo
    • domain
    • domainpass
    • domainpassword
    • eric
    • exchange
    • fred
    • fuck
    • george
    • god
    • guest
    • hallintovirikailijat
    • hell
    • hello
    • home
    • homeuser
    • ian
    • ibm
    • internet
    • intranet
    • jen
    • joe
    • john
    • kate
    • katie
    • lan
    • lee
    • linux
    • login
    • loginpass
    • luke
    • mail
    • main
    • mary
    • mike
    • neil
    • nokia
    • none
    • null
    • oem
    • oeminstall
    • oemuser
    • office
    • oracle
    • orainstall
    • outlook
    • owner
    • pass
    • pass1234
    • passwd
    • password
    • password1
    • peter
    • pwd
    • qaz
    • qwe
    • qwerty
    • rendszergazda
    • sam
    • server
    • sex
    • siemens
    • slut
    • sql
    • sqlpassoainstall
    • staff
    • student
    • sue
    • susan
    • system
    • teacher
    • technical
    • test
    • unix
    • user
    • web
    • win2000
    • win2k
    • win98
    • windows
    • winnt
    • winpass
    • winxp
    • www
    • wwwadmin
    • zxc

      Note: This step may result in user accounts being locked out due to multiple failed authentication attempts.

  24. May spread by exploiting the following vulnerabilities:

  25. May download and execute remote files, including updates of the worm.

  26. May check if it is running under the context of a debugger or VMWare. The worm terminates immediately if this is the case.

  27. May drop Hacktool.Rootkit to hide the worm from the process list.

  28. Searches for the email addresses in files that have the following extensions:

      • .wab
      • .adb
      • .tbb
      • .dbx
      • .asp
      • .php
      • .sht
      • .htm

        The worm avoids sending itself to email addresses containing the following strings:

      • .edu
      • .gov
      • .mil
      • accoun
      • acketst
      • admin
      • anyone
      • arin.
      • avp
      • be_loyal
      • berkeley
      • borlan
      • bsd
      • bugs
      • certific
      • contact
      • example
      • feste
      • fido
      • foo.
      • fsf.
      • gnu
      • gold-certs
      • google
      • gov.
      • help
      • hotmail
      • iana
      • icrosof
      • icrosoft
      • ietf
      • info
      • inpris
      • isc.o
      • isi.e
      • kernel
      • linux
      • listserv
      • math
      • mit.e
      • mozilla
      • msn.
      • mydomai
      • nobody
      • nodomai
      • noone
      • not
      • nothing
      • ntivi
      • page
      • panda
      • pgp
      • postmaster
      • privacy
      • rating
      • rfc-ed
      • ripe.
      • root
      • ruslis
      • samples
      • secur
      • sendmail
      • service
      • site
      • soft
      • somebody
      • someone
      • sopho
      • submit
      • support
      • syma
      • tanford.e
      • the.bat
      • unix
      • usenet
      • utgers.ed
      • webmaster
      • you
      • your

  29. Attempts to send a copy of itself via email using its own SMTP engine. The email may have the following characteristics:

    From: Spoofed

    One of the following:

      • hello
      • hi
      • error
      • status
      • test
      • Mail Transaction Failed
      • Mail Delivery System
      • (No Subject)
      • (random alphabets)

      One of the following:
      • The message cannot be represented in 7-bit ASCII encoding and has been sent as a binary attachment.
      • Mail transaction failed. Partial message is available.
      • test
      • The message contains Unicode characters and has been sent as a binary attachment.
      • (No body)
      • (Random data)

      May contain one of the following:

      • body
      • data
      • doc
      • document
      • file
      • message
      • readme
      • test
      • (random alphabets)

        with one of the following extensions:

      • .bat
      • .cmd
      • .exe
      • .pif
      • .scr
      • .zip

        If the attachment is a .zip file, a copy of the worm will have a second extension, which will be one of the following:

      • .doc
      • .txt
      • .htm
      • .html


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 W32.Mytob@mm Removal Tool
Symantec Security Response has developed a removal tool to clean the infections of W32.Mytob@mm. Use this removal tool first, as it is the easiest way to remove this threat.

Manual Removal:
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, and delete all files detected.
  4. Delete the value that was added to the registry.
  5. Reenable the SharedAccess service (Windows 2000/XP only)
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:
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: 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 Virus Definitions (LiveUpdate).
  • 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. To determine whether definitions for this threat are available by the Intelligent Updater, refer to Virus Definitions (Intelligent Updater).

    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 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. Note any files detected, click Delete.

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 the following subkeys:


  5. In the right pane, delete any values that refer to the file names that were detected.

  6. Navigate to the subkey:


  7. In the right pane, reset the original value, if known:

    "Start" = "4"

  8. Navigate to the subkey:


  9. In the right pane, reset the original value, if known:

    "restrictanonymous" = "1"

  10. Navigate to the subkey:


  11. In the right pane, reset the original values, if known:

    "AutoShareWks" = "0"
    "AutoShareServer" = "0"

  12. Navigate to the subkey:


  13. In the right pane, reset the original value, if known:

    "DoNotAllowXPSP2" = "1"

  14. Navigate to the subkey:


  15. In the right pane, reset the original value, if known:

    "EnableDCOM" = "N"

  16. Exit the Registry Editor.

5. To reenable the SharedAccess service (Windows 2000/XP only)
The SharedAccess service is responsible for maintaining Internet Connection Sharing and the Windows Firewall/Internet Connection Firewall applications in Windows. (The presence and names of these applications vary depending on the operating system and service pack you are using.) To protect your computer and maintain network functionality, re-enable this service if you are using any of these programs.

Windows XP Service Pack 2
If you are running Windows XP with Service Pack 2 and are using the Windows Firewall, the operating system will alert you when the SharedAccess service is stopped, by displaying an alert balloon saying that your Firewall status is unknown. Perform the following steps to ensure that the Windows Firewall is re-enabled:
  1. Click Start > Control Panel.

  2. Double-click the Security Center.

  3. Ensure that the Firewall security essential is marked ON.

    Note: If the Firewall security essential is marked on, your Windows Firewall is on and you do not need to continue with these steps.

    If the Firewall security essential is not marked on, click the "Recommendations" button.

  4. Under "Recommendations," click Enable Now. A window appears telling you that the Windows Firewall was successfully turned on.

  5. Click Close, and then click OK.

  6. Close the Security Center.

Windows 2000 or Windows XP Service Pack 1 or earlier
Complete the following steps to re-enable the SharedAccess service:
  1. Click Start > Run.
  2. Type services.msc

    Then click OK.

  3. Do one of the following:
    • Windows 2000: Under the Name column, locate the "Internet Connection Sharing (ICS)" service and double-click it.
    • Windows XP: Under the Named column, locate the "Internet Connection Firewall (ICF) / Internet Connection Sharing (ICS)" service and double-click it.

  4. Under "Startup Type:", select "Automatic" from the drop-down menu.

  5. Under "Service Status:", click the Start button.

  6. Once the service has completed starting, click OK.

  7. Close the Services window.

Writeup By: Takayoshi Nakayama