FRISK Software International

Summary of VBS/Freelink
Discovered: 15 Jul 1999
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Brief description
Technical description

Brief Description
VBS/Freelink is an e-mail worm written with the VBScript language. Programs written with VBScript operate only under Windows 98 and Windows 2000 (unless Windows Scripting Host has been installed separately).

Technical Description
VBS/Freelink does not work at all under default Windows 95 and Windows NT 4.0 installations. However, it does work under 95 and NT 4 provided that other supporting software (such as Microsoft Internet Explorer v5.x) has been installed.

Freelink was found in the wild in Europe in July 1999. This worm uses similar encryption method to the VBS/Luser viruses (they are known also as Zulu).

When the worm is executed, it drops an encrypted script file to "C:\Windows\System\Rundll.vbs". After that VBS/Freelink changes the registry in a such way that "Rundll.vbs" will be executed each time when the system is restarted.

Next, the worm shows a dialog box with the following text:

    This will add a shortcut to free XXX links on your desktop. Do you
    want to continue?
If user presses the "Yes" button, the worm creates an Internet shortcut named "FREE XXX LINKS" to the desktop. The shortcut points to web site.

The worm also searches for mapped network shares. If the worm can find any, it copies itself to the root of the each network share.

The worm uses Outlook application to mass-mail itself to each recipient in each address book. The mass-mail part is similar to W97M/Melissa, but this one doesn't infect Word documents and it sends itself each time when it is executed.

The subject of the message is:

    Check this
and the body of the message is:

    Have fun with these links.
The worm attachs itself as "Links.vbs" to the message. When the receiver double-clicks on the attachment, the worm executes and it will mass-mail itself again.

VBS/Freelink removes the sent mail from user's "Sent Mail" folder. In that way it tries to hide the mass mail from the user.

As address books typically contain group addresses, the end result of executing the Freelink worm inside an organization is that the first infected user sends the message to everybody in the organization. After this, other users open the message and send the message AGAIN to everyone else. This quickly overloads e-mail servers.

After the machine has been restarted, the worm drops "Links.vbs" to the Windows directory.

The worm will also search for "C:\MIRC" directory for "MIRC32.EXE" IRC chat client. If the executable is found, the worm creates "SCRIPT.INI" file, replacing the existing one. It also searches for another IRC client from directory "c:\PIRCH98" and if it is found, the worm replaces the "EVENTS.INI" from the same directory.

After that both IRC clients, mIRC and Pirch98, will automatically spread the worm when the user enters IRC chat channels.

[Analysis: Katrin Tocheva & Sami Rautiainen, F-Secure]

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