Threat description




NetSky.T worm was discovered on April 6th, 2004. This variant is very close to the Netsky.S variant. Like the .S variant, it has a limited set of features. The worm spreads in e-mails, but does not spread to local network and P2P and does not uninstall Bagle worm. The worm has a backdoor that listens on port 6789.


Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.

More scanning & removal options

More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.

You may also refer to the Knowledge Base on the F-Secure Community site for further assistance.

Eliminating a Local Network Outbreak

If the infection is in a local network, please follow the instructions on this webpage:

Technical Details

The worm's file is a PE executable 18432 bytes long packed with PE-Patch and UPX file compressors. Some of the worm's text strings are encrypted.

Installation to system

Upon execution NetSky.T copies itself as EastAV.exe file to Windows folder and adds a startup key for this file into System Registry:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]  "EasyAV" = "%WinDir%\EasyAV.exe"  

where %WinDir% represents Windows folder name.

Additionally the worm drops the uinmzertinmds.opm file in Windows folder. This file contains the MIME-encoded copy of the worm's executable that will be sent in e-mails.

The worm always has 2 of its processes in Windows memory. If one process gets killed, the remaining one restarts it. The worm also protects its file and startup key in the Registry from being deleted. All the above makes manual disinfection a challenging task.

Spreading in e-mail

Before spreading in e-mail the worm collects e-mail addresses. It scans all files on all drives from C: to Z: except CD-ROM drives. If any file with the following extensions is found, the worm opens it and searches for e-mail addresses there:

.eml  .txt  .php  .cfg  .mbx  .mdx  .asp  .wab  .doc  .vbs  .rtf  .uin  .shtm  .cgi  .dhtm  .adb  .tbb  .dbx  .pl  .htm  .html  .sht  .oft  .msg  .ods  .stm  .xls  .jsp  .wsh  .xml  .mht  .mmf  .nch  .ppt  

The worm spreads itself in e-mails It sends messages with different subject lines, body text and attachment names. Here's the list of subjects that the worm uses:

Hi  Hello  Re: Hi  Re: Hello  Approved  Re: Approved  Thank you!  Re: Thanks you!  Request  Re: Request  Your document  Re: Your document  Your details  Re: Your details  Your information  Re: Your information  My details  Re: My details  Important  Re: Important  

The message body is composed from 3 different string arrays:


Hi!  Hello!  Hello!  


Please read the .  Please have a look at the .  Here is the .  The  is attached.  Please see the .  I have sent the .  The requested  is attached!  Here is the document.  See the document for details.  Please have a look at the attached document.  Please read the attached document.  Your file is attached to this mail.  Please, .  Your  is attached.  My  is attached.  I have found the .  Approved, here is the document.  For more information see the attached document.  For more details see the attached document.  Please read quickly.  Please notice the attached document.  Please notice the attached .  Your .  I have spent much time for your document.  I have spent much time for the .  The .  My .  Note that I have attached your document.  


Thanks  Thank you  Yours sincerely  

The attachment name is selected and the <string> value for the message body is selected from the following variants:

approved file  list  corrected document  archive  abuse list  presentation document  instructions  details  improved document  note  message  contact list  number list  file  secound document  improved file  user list  textfile  new document  text  information  info  word document  excel document  powerpoint document  detailed document  homepage  letter  mail  document  old document  approved document  movie document  picture document  summary  description  requested document  notice  bill  answer  release  final version  diggest  important document  order  photo document  personal message  phone number  e-mail  icq number  report  story  concept  developement  sample  postcard  account  

The infected attachment has .PIF extension and can also contain random numbers in its name. The worm does not spread itself from 13th to 17th of April 2004.


The worm has a backdoor that listens on TCP port 6789. It allows to download and execute files on an infected computer.


Netsky.T has a payload. It performs a DoS (Denial of Service) attack on the following websites from 14th to 23rd of April 2004:  
Additional Info

This worm variant also contains a message from the author of the worm. Bagle is not mentioned there and taking into account that Netsky doesn't uninstall Bagle any longer, we consider the war to be over (at least for now).

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