AntiBTC

The original mail looked like this:

Date: Mon, 25 Jan 1999 20:00:26 -0500
From: "Microsoft Internet Explorer Support" IEsupport@microsoft.com
To: "Microsoft Internet Explorer User"
Subject: Please Upgrade Your Internet Explorer
  Microsoft Corporation
  1 Microsoft Way
  Redmond, WA 98052
  US

  Dear Sir/Madam
As an user of the Microsoft Internet
Explorer, Microsoft Corporation provides
you with this upgrade for your web browser.
It will fix some bugs found in your Internet
Explorer. To install the upgrade, please save
the attached file (ie0199.exe) in some folder
and run it.
For more information, please visit our
web site at www.microsoft.com/ie/
--------------------------------------------------------
(c) 1995-1998 Microsoft Corporation. All Rights Reserved  

When the IE0199.EXE file is run, it extracts two files from its body (MPREXE.DLL and SNDVOL.EXE) and copies them to the Windows system directory. Note: the MPREXE.EXE executable file (not a DLL) is one of the standard Windows file.

The trojan then registers the MPREXE.DLL file in the system to force the system to run this file on each reboot. The registration is done depending on the Windows version either in the system registry, or in the SYSTEM.INI file in [boot] section in the "drivers=" string. The MPREXE.DLL file is pointed as auto-executed.

When executed the MPREXE.DLL file just executes the SNDVOL.EXE file and exits. The SNDVOL.EXE file enables auto-dialing by changing the system registry Internet options, randomly selects one of three Bulgarian Web servers (www.btc.bg, www.infotel.bg, ns.infotel.bg), connects them and sleeps for some time. The trojan does not perform any other actions.

As a result, the trojan causes lots of network traffic both inside the infected company and at the Bulgarian servers. The trojan has probably been written to cause denial-of-service attacks for the Bulgarian systems.

Variant:PHO.EXE

PHOTOS17.EXE

This is the same trojan as described above, but it has been distributed with different names - and within different emails. Here's one sample email:

Date:
 Sat, 6 Mar 1999 07:24:32 +0200 (EET)
From:
 Lidia Steward LidiaSt27@aol.com
To:friends
Subject:
photos
Hi,
Look at the photos we talked about. I have archived them with WinZip.
Lidia
Attachment: pho.exe

Apparently, such messages have been sent to thousands of unsuspecting internet users with a mass-mailing program. The pho.exe file is a extracting executable that will drop the same AntiBTC trojan as described above.

Do not open email attachments sent by strangers.