Threat Description



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


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.


Automatic action

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


You may wish to refer to the Support Community for further assistance. You also may also refer to General Removal Instructions for a general guide on alternative disinfection actions.

Eliminating a Local Network Outbreak

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

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:

 "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:


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:


The message body is composed from one the following strings:

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

The attachment name is selected from the following variants:

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


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


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


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