Threat description




The Netsky.N variant was discovered on March 16th 2004. The worm is similar to its predecessors in the family. The only major difference is that a fake note claiming the message to be virus free is added to the infected messages.


Automatic action

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

More scanning & removal options

More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.

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

Contact Support

F-Secure customers can request support online via the Request support or the Chat forms on our Home - Global site.

Technical Details

System Infection

Upon execution the worm copies itself to the Windows System Directory with the filename 'VisualGuard.exe' which is added to the registry as

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run] =

"NetDy" = "%SysDir%\VisualGuard.exe"

The worm removes several registry values that belong to other worms.

Email Propagation

When collecting addresses NetSky.N recursively walks through all hard drives and checks the content of files with the following extensions:


The email messages are randomly composed from different components. For example the subjects are made of the following texts:

"Re: Re:"
"your "
"my "
"approved "
"important "
"word document"
 "excel document"
"read it immediately"

Email bodies are chosen from many different predefined texts:

"Please see the attached file for details."
"Please read the attached file."
"Your document is attached."
"Please read the document."
"Your file is attached."
"Your document is attached."
"Please confirm the document."
"Please read the important document."
"See the file."
"Requested file."
"Authentication required."
"Your document is attached to this mail."
"I have attached your document."
"I have received your document. The corrected document is attached."
"Your document."
"Your details."

The attachment names are hardcoded and can be one of

"doc.txt [lots of spaces].exe"
"document.htm[lots of spaces].scr"
"your_details.doc[lots of spaces].exe"

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