NetSky.Z

Summary

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NetSky.Z worm was found on April 21st, 2004. This variant is very close to previous Netsky variants. 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 665.

Removal

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Automatic action

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

More

Detailed instructions for F-Secure security products are available in the documentation found in the Downloads section of our Home - Global site.

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

Technical Details

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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 e-mails.

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:

.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 e-mails 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