Threat Descriptons



Category :


Type :


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 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.


Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note: You need administrative rights to change the settings.

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 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:


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:


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:

[lots of spaces]
[lots of spaces]
[lots of spaces]
[lots of spaces]
[lots of spaces]
[lots of spaces]
[lots of spaces]
[lots of spaces]


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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