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Discovered: April 07, 2004
Updated: February 13, 2007 12:55:57 PM
Also Known As: W32/Netsky.u@MM [McAfee], W32/Netsky-U [Sophos], WORM_NETSKY.U [Trend], Win32.Netsky.U [Computer Assoc
Type: Worm
Systems Affected: Windows

W32.Netsky.U@mm is a mass-mailing worm and a variant of W32.Netsky.S@mm . This worm also contains backdoor functionality and may perform a Denial of Service (DoS) attack against predetermined Web sites.

The Subject and Attachment name vary. The attachment has a .pif file extension.

Antivirus Protection Dates

  • Initial Rapid Release version April 08, 2004
  • Latest Rapid Release version May 31, 2016 revision 036
  • Initial Daily Certified version April 08, 2004
  • Latest Daily Certified version June 01, 2016 revision 005
  • Initial Weekly Certified release date April 14, 2004

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

Writeup By: Yana Liu

Discovered: April 07, 2004
Updated: February 13, 2007 12:55:57 PM
Also Known As: W32/Netsky.u@MM [McAfee], W32/Netsky-U [Sophos], WORM_NETSKY.U [Trend], Win32.Netsky.U [Computer Assoc
Type: Worm
Systems Affected: Windows

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

  1. Copies itself as %Windir%\SymAV.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.

  2. Creates a mutex, "SyncMutex_USUkUyUnUeUtUU," to allow only one instance of the worm to execute.

  3. Creates the file, %Windir%\fuck_you_bagle.txt, which is a MIME-encoded copy of the worm's executable.

  4. Adds the value:


    to the registry key:


    so that the worm runs when you start Windows.

  5. Listens on port 6789. If an attacker sends an executable file to an infected computer, the worm will save it as an executable file with a random file name, and then execute the file.

  6. If the computer's system date is between April 14, 2004 to April 23, 2004, the worm will attempt a DoS attack against the following Web sites:
    • www.cracks.am
    • www.emule.de
    • www.kazaa.com
    • www.freemule.net
    • www.keygen.us

  7. Scans drives C through Z (excluding the CD-ROM drives) and retrieves the email addresses from the files with the following extensions:
    • .asp
    • .cfg
    • .cgi
    • .dbx
    • .dhtm
    • .doc
    • .eml
    • .htm
    • .html
    • .jsp
    • .mbx
    • .mdx
    • .mht
    • .mmf
    • .msg
    • .nch
    • .ods
    • .oft
    • .php
    • .pl
    • .ppt
    • .rtf
    • .sht
    • .shtm
    • .stm
    • .tbb
    • .txt
    • .uin
    • .vbs
    • .wab
    • .wsh
    • .xls
    • .xml

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

    : <Spoofed>

    Subject: (One of the following)
    • Re: Hi
    • Re: Hello
    • Hi
    • Hello
    • Hey
    • It's me
    • Again
    • Reply
    Message: (One of the following)
    • Oh, I got it!
    • To less characters! Take it easy...
    • I noticed your password for administrative purpuses.
    • Yet another password! Need a better one?
    • Oh... your password!
    • Need a better password? my advice....
    • Your pwd is critical, too short, to low!
    • Do not use personal information for your password!
    • Your password on a website?
    • Passwordlist? yours?
    • I needed only 2 hours to get your password.
    • Change your password! I have stolen some text, excuse me!
    • Dictionary attacks are good. Your password not!
    • I used the brute-force method to get your password..
    • Take it easy... Your password is too short.
    • I've got your password! take it easy...
    • Hey, easy passwords!
    • Oh! Excuse me, your password is too easy!!!
    • Not with me!
    • Here is a sample of your private documents I have stolen!
    • Your privacy! lol, youre not protected!
    • Needed? No, here I give it back!
    • I believe from the document you are a child!
    • Check your document, errors are there!
    • Please, please, Give me another sexy document about you!
    • Short and good, your document!
    • Jooooooooo.... document? Yours????? Wehaaa!
    • I do not accept documents from bad guys!
    • I do not want your document!
    • Go to hell an burn with your bad document!
    • I will send your list to the police!!!!
    • Hello, here.
    • It's the truth, your document not!!!
    • Could I have more texts about you?
    • Thus is enough. Stop sending your Sh*tty documents!!!
    • One, two three, more, I have many questions to you document!'
    • Nice, nice, more and more? do you?
    • Should I believe it? No, however, your story is bad.
    • Oh.....puh, your story is very strong!
    • Yours is very nice!
    • Do you have more of that?
    • Hey ya, nice document. Do you have more?
    • Abou you?
    • Sexy pic abou you?
    • Do you have a digicam to make your private photos?
    • More naked...your body is sexy!
    • Naked, you?
    • Are you naked?
    • More private photos of you? no!
    • Private photos...mmmhh. I like it. Post me more please!
    • Hey, naked one!
    • Hey, have you ever seen your photo?
    • Eat my Sh*t! Your photo is bad.
    • Do not distribute your naked photos!
    • Uhaaa! naked... are you cranky?
    • Your are naked? Tell me more...please!
    • Hey, private or private..naked?
    • Pah!...take your private photo, naked and so, and go away.
    • I have sent your private photo to the police.
    • What is when I show your private illegal photo the police?
    • You? Very funny! More available?
    • I don't want to see your photo!
    • Sh*t... your photo! naked?

    (One of the following)
    • yours_funny
    • yours_naked_img
    • not_permitted
    • img05
    • yours_naked
    • yoursnaked
    • yourphoto
    • yourimage
    • yours
    • pic04
    • yournakedpic
    • yourpic
    • yourphoto
    • private
    • your_private_document
    • xxx_yours_naked
    • your_bad_photo
    • about_you
    • private_photo
    • private_pic
    • your_photo
    • photo03
    • document
    • private
    • yourdoc
    • yourdocument
    • mydocument
    • onedocument
    • your_doc04
    • founddocument
    • document3
    • anotherdocument
    • document_part
    • alldoc
    • details
    • shortdoc
    • doc04
    • illegaldocument
    • abusedocument
    • posteddocument
    • trieddocument
    • yetanotherdocument
    • doc
    • sexydocument
    • letter
    • story
    • mail
    • abuses
    • morestory
    • doc_ed
    • approvdoc
    • detailed
    • listed
    • correct_pass
    • pass01
    • pwds04
    • password02
    • pwd
    • yourspwd
    • your_pwd
    • your_password
    • pwd_list
    • passwords
    • password
    • yourpassword
    • easypassword
    • cracked_password
    • morepasswords

    • The attachment has a .pif extension.
    • The worm may also send an email message to hanta@chiva.net.


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: April 07, 2004
Updated: February 13, 2007 12:55:57 PM
Also Known As: W32/Netsky.u@MM [McAfee], W32/Netsky-U [Sophos], WORM_NETSKY.U [Trend], Win32.Netsky.U [Computer Assoc
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 VGA mode.
  4. Run a full system scan and delete all the files detected as W32.Netsky.U@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.U@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: Yana Liu