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Worm:W32/NetSky.F

Classification

Category: Malware

Type: Email-Worm

Aliases: NetSky.F, W32/NetSky.F@mm, I-Worm.NetSky.f, W32.Netsky.F@mm

Summary


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

Removal


Automatic action

Once detected, the F-Secure security product will automatically handle a harmful program or file by either deleting or renaming it.

Eliminating a Local Network Outbreak

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

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Submit a sample

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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: https://www.f-secure.com/virus-info/v-pics/netsky_d.wav

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[SkyNet.cz]SystemsMutex" to avoid running more than one instance of itself.

Spreading in emails

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

The worm scans all available drives except CD-ROM drives for emails. It searches for email 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 emails to email 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.