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Worm:W32/NetSky.Z

Classification

Category: Malware

Type: Email-Worm

Aliases: NetSky.Z, W32/NetSky.Z@mm, I-Worm.Netsky.aa, Netsky.Z

Summary


NetSky.Z worm was found on April 21st, 2004. This variant is very close to previous Netsky variants. The worm spreads in emails, but does not spread to local network and P2P and does not uninstall Bagle worm. The worm has a backdoor that listens on port 665.

Removal


Automatic action

Based on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the detected program or file, or ask you for a desired action.

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Technical Details


The worm's file is a PE executable 22016 bytes long packed with a new or modified file compressor. Some of the worm's text strings are encrypted.

Installation to system

Upon execution NetSky.Z copies itself as Jammer2nd.exe file to Windows folder and adds a startup key for this file into System Registry:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]
"Jammer2nd" = "%WinDir%\Jammer2nd.exe"

where %WinDir% represents Windows folder name.

Additionally the worm creates a few files with .LOG extension in Windows folder. These files contain binary and MIME-encoded copies of the worm's executable that will be sent in emails.

Spreading in email

Before spreading in email the worm collects email 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 email addresses there:

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

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

Important
Document
Hello
Information
Hi

The message body is composed from one the following strings:

Important details!
Important notice!
Important document!
Important bill!
Important data!
Important!
Important textfile!
Important informations!

The attachment name is selected from the following variants:

Details.zip
Notice.zip
Important.zip
Bill.zip
Data.zip
Part-2.zip
Textfile.zip
Informations.zip

The ZIP attachments contain worm's executables with one of the following names:

Informations.txt
[lots of spaces]
 .exe
Textfile.txt
[lots of spaces]
 .exe
Part-2.txt
[lots of spaces]
 .exe
Data.txt
[lots of spaces]
 .exe
Bill.txt
[lots of spaces]
 .exe
Important.txt
[lots of spaces]
 .exe
Notice.txt
[lots of spaces]
 .exe
Details.txt
[lots of spaces]
 .exe
Backdoor

The worm has a backdoor that listens on TCP port 665. It allows to download and execute files on an infected computer.

Payload

NetSky.Z has a payload. It performs a DoS (Denial of Service) attack on the following websites from 2nd to 5th of May, 2004:

www.educa.ch
www.medinfo.ufl.edu
www.nibis.de