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W32/Netsky.N, I-Worm.Netsky.n



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.

Disinfection & Removal

Automatic Disinfection

Allow F-Secure Anti-Virus to disinfect the relevant files.

For more general information on disinfection, please see Removal Instructions.

Eliminating a Local Network Outbreak

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

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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