Threat Description



Category: Malware
Platform: W32
Aliases: Gribble, Trojan.IRC.Gribble, JBGR


Gribble is a trojan that has been available an a web page that uses a Java Virtual Machine vulnerability in Internet Explorer to drop and execute the worm.

Further infromation about the vulnerability, including a fix, is available from Microsoft:


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

When the trojan is executed, it creates "jb.vbs" file into the root of the current drive. This file is executed.

Afther that the trojan drops another VBS file, "C:\lipreffs.vbs". This file is executed as well when it adds itself to to the registry in a such way that it is executed when the system is restarted. It also starts to send large ICMP echo (ping) packets to the

Next Gribble goes trough all drives, and if it is able to locate a mIRC installation, it will create "script.ini" and modify the "mirc.ini" so, that it will be loaded when the IRC client is started.

Finally the trojan deletes "c:\jb.vbs".

The modified "script.ini" will attempt a Denial of Service attack agains when a connection is made with the mIRC client. DoS attack consists of random HTTP requests to either or, and garbage sent to the DNS server.

Further the trojan sends offensive messages when another user joins a channel where the infected user is.

Technical Details:Katrin Tocheva and Sami Rautiainen, F-Secure; September 2001


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