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Discovered: April 21, 2005
Updated: February 13, 2007 12:37:34 PM
Also Known As: Win32.Mytob.BU [Computer Assoc, Net-Worm.Win32.Mytob.gen [Kasp, W32/Mytob.gen@MM [McAfee], W32/Mytob-Fam [Sophos], WORM_MYTOB.CH [Trend Micro]
Type: Worm
Systems Affected: Windows

W32.Mytob.BH@mm is a mass-mailing worm that has back door capabilities and uses its own SMTP engine to send an email to addresses that it gathers from the compromised computer.

The worm spreads through the network by exploiting the Microsoft Windows Local Security Authority Service Remote Buffer Overflow (as described in Microsoft Security Bulletin MS04-011) and the Microsoft Windows DCOM RPC Interface Buffer Overrun Vulnerability (described in Microsoft Security Bulletin MS03-026).

Removing entries from the Hosts file
If this threat has modified the Windows Hosts file, there are two ways to remove these entries:

  • Install and run the current version of LiveUpdate. This will remove only the entries that refer to Symantec domains.
  • Manually edit the Hosts file and remove all the entries that the threat added.

To run the current version of LiveUpdate
  1. Click download LiveUpdate.

    If you are not reading this Web page on the computer that is getting the error notice, the address for downloading the file is:


    If necessary, you can type this address into the address bar of the problem computer. Changes to the Hosts file will not stop you from getting to this site.

  2. Save the file to the Windows desktop.
  3. Double-click the lusetup.exe icon on the desktop to install LiveUpdate.
  4. Run LiveUpdate.
  5. Did you see the message "LU1860: LiveUpdate has detected a potential security compromise on your computer"?
    • If you did, let LiveUpdate "Remove these entries from the hosts files" (Recommended).
      This should allow LiveUpdate to run.
    • If you did not, that was not the cause of the problem. Return to the Removal section.

To manually edit the Hosts file and remove all the entries that the worm added

Note: The location of the Hosts file may vary and some computers may not have this file. For example, if the file exists in Windows 98, it will usually be in C:\Windows; and it is located in the C:\WINNT\system32\drivers\etc folder in Windows 2000. There may also be multiple copies of this file in different locations.

Follow the instructions for your operating system:
  • Windows 95/98/Me/NT/2000
    1. Click Start, point to Find or Search, and then click Files or Folders.
    2. Make sure that "Look in" is set to (C:) and that "Include subfolders" is checked.
    3. In the "Named" or "Search for..." box, type:


    4. Click Find Now or Search Now.
    5. For each Hosts file that you find, right-click the file, and then click Open With.
    6. Deselect the "Always use this program to open this program" check box.
    7. Scroll through the list of programs and double-click Notepad.
    8. When the file opens, delete all the entries in step 11 of the "Technical Details" section.
    9. Close Notepad and save your changes when prompted.

  • Windows XP
    1. Click Start > Search.
    2. Click All files and folders.
    3. In the "All or part of the file name" box, type:


    4. Verify that "Look in" is set to "Local Hard Drives" or to (C:).
    5. Click More advanced options.
    6. Check Search system folders.
    7. Check Search subfolders.
    8. Click Search.
    9. Click Find Now or Search Now.
    10. For each Hosts file that you find, right-click the file, and then click Open With.
    11. Deselect the Always use this program to open this program check box.
    12. Scroll through the list of programs and double-click Notepad.
    13. When the file opens, delete all the entries in step 11 of the "Technical Details" section.
    14. Close Notepad and save your changes when prompted.

Antivirus Protection Dates

  • Initial Rapid Release version April 22, 2005
  • Latest Rapid Release version March 03, 2008 revision 035
  • Initial Daily Certified version April 22, 2005
  • Latest Daily Certified version March 03, 2008 revision 037
  • Initial Weekly Certified release date April 27, 2005

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

Writeup By: Ka Chun Leung

Discovered: April 21, 2005
Updated: February 13, 2007 12:37:34 PM
Also Known As: Win32.Mytob.BU [Computer Assoc, Net-Worm.Win32.Mytob.gen [Kasp, W32/Mytob.gen@MM [McAfee], W32/Mytob-Fam [Sophos], WORM_MYTOB.CH [Trend Micro]
Type: Worm
Systems Affected: Windows

When W32.Mytob.BH@mm is executed, it performs the following actions:

  1. Copies itself as the following:

    • %System%\taskgmrs.exe
    • C:\my_photo2005.scr
    • C:\see_this!!.scr
    • C:\funny_pic.scr

      Note: %System% is a variable that refers to 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).

  2. Creates the following file which is detected as W32.Mytob.L@mm:


  3. Adds the value:

    "WINTASK" = "taskgmr.exe"

    to the registry subkey:


    so that W32.Mytob.BB@mm runs every time Windows starts.

    Note: The worm will recreate these registry subkeys if they are deleted.

  4. Creates the following mutex so that only one instance of the worm is run on the compromised computer:


  5. Gathers email addresses from the Windows Address Book and from the following locations:

    • %Windir%\Temporary Internet Files
    • %UserProfile%\Local Settings\Temporary Internet Files
    • %System%

    • %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows or C:\Winnt.
    • %UserProfile% is a variable that refers to the current user's profile folder. By default, this is C:\Documents and Settings\<Current User> (Windows NT/2000/XP).

      The worm gathers email addresses from files with the following extensions on all local drives from C to Y:

    • .adb*
    • .asp*
    • .dbx*
    • .htm*
    • .php*
    • .pl
    • .sht*
    • .tbb*
    • .txt
    • .wab*

      The worm will not send itself to email addresses that contain any of the following strings:

    • abuse
    • accoun
    • acketst
    • admin
    • anyone
    • arin.
    • avp
    • bugs
    • ca
    • certific
    • contact
    • example
    • feste
    • fido
    • foo.
    • fsf.
    • gnu
    • gold-certs
    • google
    • help
    • info
    • linux
    • listserv
    • me
    • no
    • nobody
    • noone
    • not
    • nothing
    • ntivi
    • page
    • postmaster
    • privacy
    • rating
    • root
    • samples
    • service
    • site
    • soft
    • somebody
    • someone
    • submit
    • support
    • the.bat
    • unix
    • webmaster
    • you
    • your

      The worm will not send itself to email addresses that contain any of the following strings in the domain name:

    • .edu
    • .gov
    • .mil
    • arin.
    • berkeley
    • borlan
    • bsd
    • example
    • fido
    • foo.
    • fsf.
    • gnu
    • google
    • gov.
    • iana
    • ibm.com
    • icrosof
    • icrosoft
    • ietf
    • inpris
    • isc.o
    • isi.e
    • kernel
    • linux
    • math
    • mit.e
    • mozilla
    • mydomai
    • nodomai
    • panda
    • pgp
    • rfc-ed
    • ripe.
    • ruslis
    • secur
    • sendmail
    • sopho
    • syma
    • tanford.e
    • unix
    • usenet
    • utgers.ed
    • www

      The worm may append the following prefixes to domain names in an attempt to find Simple Mail Transfer Protocol (SMTP) servers:

    • gate.
    • mail.
    • mail1.
    • mx.
    • mx1.
    • mxs.
    • ns.
    • relay.
    • smtp.

  6. Uses its own SMTP engine to send itself to the email addresses that it finds. The email has the following characteristics:

    One of the following: (spoofed)

    • [random generated letters]
    • adam
    • alex
    • andrew
    • anna
    • bill
    • bob
    • brenda
    • brent
    • brian
    • britney
    • bush
    • claudia
    • dan
    • dave
    • david
    • debby
    • fred
    • george
    • helen
    • jack
    • james
    • jane
    • jerry
    • jim
    • jimmy
    • joe
    • john
    • jose
    • julie
    • kevin
    • leo
    • linda
    • lolita
    • madmax
    • maria
    • mary
    • matt
    • michael
    • mike
    • peter
    • ray
    • robert
    • sam
    • sandra
    • serg
    • smith
    • stan
    • steve
    • ted
    • tom

      with one of the following domains:

    • aol.com
    • cia.gov
    • fbi.gov
    • hotmail.com
    • juno.com
    • msn.com
    • yahoo.com

      One of the following:

    • hello
    • Good Day
    • Error
    • Mail Delivery System
    • Mail Transaction Failed
    • Server Report
    • Status

      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.
    • The original message was included as an attachment.
    • I have received your document. The corrected document is attached.
    • Here are your banks documents

      One of the following:

    • body
    • data
    • doc
    • document
    • file
    • message
    • readme
    • test
    • text

      with one of the following extensions:

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

      Note: The attachment may also be a .zip file containing a copy of the worm with two file extensions. The copy of the worm will have .doc, .htm, or .txt as the first extension, and .exe, .pif, or .scr as the second extension.

  7. Connects to an IRC channel on the njbv.gotdns.com domain.

  8. Listen for commands that allow the remote attacker to perform the following actions:

    • Execute files
    • Download files
    • Perform other IRC commands determined by the attacker
    • Reboot the compromised computer

  9. Spreads by exploiting the following vulnerabilities:

  10. If the worm successfully exploits a vulnerable computer, it may drop a file named 2pac.txt on to the newly compromised computer. This file opens port 12187 and downloads a copy of the worm as bingoo.exe.

  11. Blocks access to several security-related Web sites by appending the following text to the Hosts file:       www.symantec.com       securityresponse.symantec.com       symantec.com       www.sophos.com       sophos.com       www.mcafee.com       mcafee.com       liveupdate.symantecliveupdate.com       www.viruslist.com       www.viruslist.com       viruslist.com       f-secure.com       www.f-secure.com       kaspersky.com       www.avp.com       www.kaspersky.com       avp.com       www.networkassociates.com       networkassociates.com       www.ca.com       ca.com       mast.mcafee.com       my-etrust.com       www.my-etrust.com       download.mcafee.com       dispatch.mcafee.com       secure.nai.com       nai.com       www.nai.com       update.symantec.com       updates.symantec.com       us.mcafee.com       liveupdate.symantec.com       customer.symantec.com       rads.mcafee.com       trendmicro.com       www.microsoft.com       www.trendmicro.com


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: Ka Chun Leung

Discovered: April 21, 2005
Updated: February 13, 2007 12:37:34 PM
Also Known As: Win32.Mytob.BU [Computer Assoc, Net-Worm.Win32.Mytob.gen [Kasp, W32/Mytob.gen@MM [McAfee], W32/Mytob-Fam [Sophos], WORM_MYTOB.CH [Trend Micro]
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. Run a full system scan and delete all the files detected as W32.Mytob.BH@mm.
  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:
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 the document: 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 the document: 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.

    Note: If you see an error, such as LU1418, when you try to run LiveUpdate and you cannot get the Web site hosting the Intelligent Updater, it is likely that the worm has modified the Hosts file. You can either download and install LiveUpdate 2.5, which can remove Symantec entries from that file, or you can edit it yourself. See the instructions for both in the "Additional Information" section below.

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. If any files are detected as infected with W32.Mytob.BH@mm, click Delete.

    If your Symantec antivirus product reports that it cannot delete an infected file, Windows may be using the file. To fix 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 section 4.

    Warning messages may be displayed when the computer is restarted, as the threat has not been fully removed at this point. Please ignore these messages and just 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.

  4. Navigate to the subkeys:


  5. In the right pane, delete the value:

    "WINTASK" = "taskgmr.exe"

  6. Exit the Registry Editor.

Writeup By: Ka Chun Leung