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