Threat description




NetSky.F worm variant was found on 3rd of March 2004. This variant spreads itself in e-mails as an executable attachment.


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 following text string is present in the worm's body:

Skynet AntiVirus -  Bagle - you are a looser!!!!  

This indicates an on-going competition/war among virus writers of the currently widespread malware: Bagle and NetSky. This NetSky worm variant tries to remove Bagle worm infection if it finds it on an infected computer.

Descriptions of all previous NetSky variants can be found here:

The worm's file is a PE executable file 18432 bytes long, packed with PE-Pack file compressor. The unpacked file's size is over 28 kilobytes.

On March 2nd, 2004 the worm constantly beeps with PC speaker from 6:00 to 8:59. Below is the link to the WAV file with the sound that the worm makes:

NetSky.F worm doesn't copy its files to shared folders.

Installation to system

When run, the worm installs itself to system. It copies its file to Windows folder as SVCHOST.EXE and creates a startup key for this file in System Registry:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]  "Zone Labs Client Ex" = "%windir%\svchost.exe -antivirus service"  

where %windir% represents Windows directory

The worm creates a mutex named "LK[]SystemsMutex" to avoid running more than one instance of itself.

Spreading in e-mails

NetSky.F worm has its own SMTP engine that it uses to send emails with infected attachments to all found e-mail addresses. The worm uses different subjects, message body texts and attachment names in its e-mails.

The worm scans all available drives except CD-ROM drives for e-mails. It searches for e-mail addresses in files with the following extensions:

.dhtm  .cgi  .shtm  .msg  .oft  .sht  .dbx  .tbb  .adb  .doc  .wab  .asp  .uin  .rtf  .vbs  .html  .htm  .php  .txt  .eml  

The subject for infected messages is selected from the following list:

Re: Your website  Re: Your product  Re: Your letter  Re: Your archive  Re: Your text  Re: Your bill  Re: Your details  Re: My details  Re: Word file  Re: Excel file  Re: Details  Re: Approved  Re: Your software  Re: Your music  Re: Here  Re: Re: Re: Your document  Re: Hello  Re: Hi  Re: Re: Message  Re: Your picture  Re: Here is the document  Re: Your document  Re: Thanks!  Re: Re: Thanks!  Re: Re: Document  Re: Document  

The message body text for infected messages is selected from the following list:

Your file is attached.  Please read the attached file.  Please have a look at the attached file.  See the attached file for details.  Here is the file.  Your document is attached.  

The attachment name for infected messages is selected from the following list:

your_website.pif  your_product.pif  your_letter.pif  your_archive.pif  your_text.pif  your_bill.pif  your_details.pif  document_word.pif  document_excel.pif  my_details.pif  all_document.pif  application.pif  mp3music.pif  yours.pif  document_4351.pif  your_file.pif  message_details.pif  your_picture.pif  document_full.pif  message_part2.pif  document.pif  your_document.pif  

The worm avoids sending e-mails to e-mail addresses that contain any of the following substrings:

icrosoft  antivi  ymantec  spam  avp  f-secur  itdefender  orman  cafee  aspersky  f-pro  orton  fbi  abuse  messagelabs  skynet  andasoftwa  freeav  sophos  antivir  iruslis  
Deleting Registry keys and disinfecting Bagle worm

The NetSky.F worm variant of the worm deletes the following Registry keys:

[HKCR\CLSID\{E6FB5E20-DE35-11CF-9C87-00AA005127ED}\InProcServer32] [HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\PINF] [HKLM\System\CurrentControlSet\Services\WksPatch] [HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices]  system. [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]  KasperskyAv  Explorer  Taskmon  system.  msgsvr32  DELETE ME  service  Sentry  Windows Services Host [HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]  KasperskyAv  Explorer  OLE  Windows Services Host  d3dupdate.exe  au.exe  sysmon.exe  rate.exe  gouday.exe  

NetSky.F worm removes Registry keys of several Bagle worm variants if it finds them on an infected computer. The last 5 keys listed above belong to earlier Bagle variants.

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