Threat Description



Category: Malware
Type: Worm
Platform: W32
Aliases: Gismor, W32.Gismor@mm


Gismor is a mass-mailing worm that arrives in e-mail disguised as an MP3 player program. The worm uses the the Invalid MIME Type Vulnerability to execute the infected attachment automatically when the message is opened.


Automatic action

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

More scanning & removal options

More information on scanning or removal options is available in the documentation for your F-Secure security product on the Downloads section of our Home - Global site.

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

Contact Support

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

Technical Details

The message that Gismor sends has the following properties:

From: MP3 Deluxe  To: My best friends  Subject: Phenomenal  

The message has no text in the body and has an attachment called 'MP3Player.exe'.

When the infected attachment is run it copies itself to Windows System Directory as 'SSMS.EXE' and adds this copy to the registry as


The worm uses MAPI to list all the incoming messages and sends an infected message to each sender it finds there. It uses direct SMTP connection to send the infected messages. The SMTP settings are fetched from the first active account from the user's settings. If the worm does not find the SMTP setting in the registry it uses a predefined SMTP server.


Gismor has a payload routine that overwrites certain files (.doc, .xls, .mp3, .mdb, .htm, .asp, .dbf, .cpp, .rtf, .wav) with the worm body. Based on the first analysis this routine is never called.


For more information and the fix for the Invalid MIME Type Vulnerabilty please visit

Technical Details:Gergely Erdelyi; F-Secure Corp.; September 9th, 2002


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