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Category: Malware

Type: Email-Worm

Aliases: NetSky.O, W32/Netsky.O, I-Worm.Netsky.o


The Netsky.O variant was discovered on March 16th 2004.The O variant follows the footsteps of the earlier ones. This variant uses four different fake antivirus scanner messages mentioning four different major antivirus companies including F-Secure.


Automatic action

Once detected, the F-Secure security product will automatically handle a harmful program or file by either deleting or renaming it.

Eliminating a Local Network Outbreak

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

Knowledge Base

Find the latest advice in our Community Knowledge Base.

About the product

See the manual for your F-Secure product on the Help Center.

Contact Support

Chat with or call an expert for help.

Submit a sample

Submit a file or URL for further analysis.

Technical Details

System Infection

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

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

"MsInfo" = "%SysDir%\AVBgle.exe"

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

Email Propagation

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


Emails composed from different components randomly chosen from predefined sets.

Possible subjects:

Re: Mail Authentification
Re: Delivery Protection
Re: Secure delivery
Re: Protected Mail Delivery
Re: Protected Mail System
Re: Protected Mail Request
Re: Secure SMTP Message
Re: Extended Mail System
Re: Error
Re: Message Error
Re: Administration
Re: Test
Re: Thank you for delivery
Re: Failure
Re: Bad Request
Re: Delivery Server
Re: Mail Server
Re: SMTP Server
Re: Notify
Re: Status
Re: Extended Mail
Re: Encrypted Mail

Email bodies are chosen from:

You have received an extended message. Please read the instructions.
New message is available.
Now a new message is available.
You got a new message.
SMTP: Please confirm the attached message.
Bad Gateway: The message has been attached.
Protected message is available.
Waiting for authentification.
Protected message is attached.
Please authenticate the secure message.
Follow the instructions to read the message.
Please read the attachment to get the message.
Encrypted message is available.
Delivered message is attached.
Forwarded message is available.
Secure Mail System Beta Test.
Protected Mail System Test.
Your requested mail has been attached.
For further details see the attachment.
For more details see the attachment.
First part of the secure mail is available.
Waiting for a Response. Please read the attachment.
Partial message is available.
ESMTP [Secure Mail System #334]:
Secure message is attached.
Please confirm my request.

Attachment names can be one of


All messages end with a fake antivirus scanner message chosen from four different variants:

+++ Attachment: No Virus found
+++ Panda AntiVirus - You are protected
+++ www.pandasoftware.com
+++ Attachment: No Virus found
+++ F-Secure AntiVirus - You are protected
+++ www.f-secure.com
+++ Attachment: No Virus found
+++ Norman AntiVirus - You are protected
+++ www.norman.com
+++ Attachment: No Virus found
+++ Norton AntiVirus - You are protected
+++ www.symantec.de