Classification

Category: Malware

Type: Virus

Platform: W97M

Aliases: Cobra

Summary


Cobra.A is a Word 97 virus that contains a destructive payload.

Removal


Automatic action

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Technical Details


The virus infects when a document is opened, closed or saved. When the current date is September 11 and a document is closed, the virus inserts a small code in another module - the class module ThisDocument. This code activates when a user exits Word application. Than the virus show a message box with a tittle "Cobra" and the following contents:


 "You are infected with Cobra"

When FileSaveAs is used Cobra.A creates additional module ComCity. This code activates when a new file is created. If the date is October 11 the virus deletes all the files on "C:\" drive.


Variant:Cobra.F

Cobra.F is a mass-mailer and spreads via email as the Melissa virus.

The main part of the virus code, the replicating and the mass-mailing parts are in "BornCobra" module.

When an infected document is opened or closed the virus adds a registry key "Cobra". It changes also the registered Windows owner to "Cobra" and the registered organization to "DHK/BD". After that it replicates and executes its mass-mailing part.

Using Outlook application the virus sends an email message to the first 30 recipients from each users address book. The email message looks as follows:


 From:
(name of the infected user)
 Subject: "Important Message From Microsoft Via " (name of
 the infected user)
 Body: "Important documment"
 Attachment: (infected active document)

Cobra.F also disable the build-in macro virus protection and Tools/Macro menu.

The virus creates another module named "Cobra" that contains a destructive payload. It executes when a new file is created. If the number of the current day and month are the same, it deletes all directories from "C:" drive in a hidden DOS process.


Variant:Cobra.Z

This variant infects during opening, closing documents and exit MS Word application.

The virus uses two modules: Cobra_20C in infected global template and NewCobra (that is the same) and MoreInfect in infected documents.

The code in NewCobra (Cobra_20C) module contains the replicating code. It first removes Tools/Macro and View/Toolbars menus. Then it disables Alt/F8 and Alt/F11 that are the keys for Tools/Macro and Visual Basic Editor. This code extracts the payload of the virus that it places in MoreInfect module.

It modifies the registry to change the Windows registered owner to "Cobra" and registered organization to "349,PB/ER/DHK-1217/BD". In addition it creates a registry key to keep the date of the initial infection. If the system has been infected for more then 60 days, then during creating a new Word document the virus tries to deletes the recent file list of Excel 8.0.

On the top of its code the virus contains the following commented text:


 'Cobra Version 2.0C