Threat Description

Tam

Details

Aliases: Tam, Out, I-Worm.Kakworm.d
Category: Malware
Type: Worm
Platform: VBS

Summary


VBS/Tam is a worm similar to JS/Kak. It uses the same security vulnerability to infect the system.

Microsoft has released a patch that fixes this vulnerability. It is available at https://www.microsoft.com/security/Bulletins/ms99-032.asp .



Removal


Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.

More

Detailed instructions for F-Secure security products are available in the documentation found in the Downloads section of our Home - Global site.

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



Technical Details



Variant:Tam.A

If an infected message is viewed, the worm creates a file, "tam.hta", to the startup directory of French version of Windows 9x ("C:\Windows\Menu demarrer\programmes\demarrage"). This file is executed when the system is restarted.

When the "tam.hta" is executed, it deletes file "c:\windows\out.html" if it exists. Then the worm creates a new file using the same file name. This file contains the worm code.

Next VBS/Tam.A checks if a file "out.hta" exists in the Windows directory, and if not, it copies the "tam.hta" there and hides "tam.hta".

The copied "out.hta" will be added to the registry, so it will be executed in each time when the system is restarted.

The worm replaces the signature settings of Outlook Express 5.0 with its own, so every email sent will contain the worm.

At August 30th, the it shows the following message four times:

  Bon Anniversaire Lac !!!           Un ami...  

Depending on time user spends between the first and the last message box, the worm executes two different payloads.

The first one is activated if time is greater than 10 seconds, when the following message box is shown:

  Ok, chante HappyBirthday tout ira bien!!!  

Otherwise, VBS/Tam.A shows the following message

  KOI??? Ca t'interresse pas? Tu n'es pas digne du monde informatique. BYE-BYE  

and shuts down Windows.





Technical Details:Katrin Tocheva and Sami Rautiainen, F-Secure; October 2000


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