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Klarinet Archive - Posting 000376.txt from 1999/06

From: "Mark Charette" <>
Subj: [kl] Offtopic: New trojan horse program (CERT advisory attached)
Date: Fri, 11 Jun 1999 08:12:23 -0400

There's a new Trojan horse program out called ExploreZip - it comes as
an attachment called explore_zip.exe on a mail message. Part of the CERT
advisory (Computer Emergency Response Team) is attached.

CERT Advisory CA-99-06 ExploreZip Trojan Horse Program

Original issue date: Thursday June 10, 1999
Source: CERT/CC

Systems Affected

* Machines running Windows 95, Windows 98, or Windows NT.
* Any mail handling system could experience performance problems or
a denial of service as a result of the propagation of this Trojan
horse program.


The CERT Coordination Center continues to receive reports and
inquiries regarding various forms of malicious executable files that
are propagated as file attachments in electronic mail.

Most recently, the CERT/CC has received reports of sites affected by
ExploreZip, a Windows Trojan horse program.

I. Description

The CERT/CC has received reports of a Trojan horse program that is
propagating in email attachments. This program is called ExploreZip.
The number and variety of reports we have received indicate that this
has the potential to be a widespread attack affecting a variety of

Our analysis indicates that this Trojan horse program requires the
victim to run the attached zipped_files.exe program in order install
copy of itself and enable propagation.

Based on reports we have received, systems running Windows 95,
98, and Windows NT are the target platforms for this Trojan horse
program. It is possible that under some mailer configurations, a user
might automatically open a malicious file received in the form of an
email attachment. This program is not known to exploit any new
vulnerabilities. While the primary transport mechanism of this
is via email, any way of transferring files can also propagate the

The ExploreZip Trojan horse has been propagated in the form of email
messages containing the file zipped_files.exe as an attachment. The
body of the email message usually appears to come from a known email
correspondent, and may contain the following text:

I received your email and I shall send you a reply ASAP.
Till then, take a look at the attached zipped docs.

The subject line of the message may not be predictable and may appear
to be sent in reply to previous email.

Opening the zipped_files.exe file causes the program to execute. At
this time, there is conflicting information about the exact actions
taken by zipped_files.exe when executed. One possible reason for
conflicting information may be that there are multiple variations of
the program being propagated, although we have not confirmed this one
way or the other. Currently, we have the following general
on actions taken by the program.

* The program searches local and networked drives (drive letters C
through Z) for specific file types and attempts to erase the
contents of the files, leaving a zero byte file. The targets may
include Microsoft Office files, such as .doc, .xls, and .ppt, and
various source code files, such as .c, .cpp, .h, and .asm.
* The program propagates by replying to any new email that is
received by an infected computer. A copy of zipped_files.exe is
attached to the reply message.
* The program creates an entry in the Windows 95/98 WIN.INI file:
On Windows NT systems, an entry is made in the system registry:
run @-----.exe"
* The program creates a file called explore.exe in the following
Windows 95/98 - c:windowssystemexplore.exe
Windows NT - c:winntsystem32explore.exe
This file is a copy of the zipped_files.exe Trojan horse, and the
file size is 210432 bytes.
MD5 (Explore.exe) = 0e10993050e5ed199e90f7372259e44b

We will update this advisory with more specific information as we are
able to confirm details. Please check the CERT/CC web site for the
current version containing a complete revision history.

II. Impact

* Users who execute the zipped_files.exe Trojan horse will infect
the host system, potentially causing targeted files to be
* Indirectly, this Trojan horse could cause a denial of service on
mail servers. Several large sites have reported performance
problems with their mail servers as a result of the propagation
this Trojan horse.

III. Solution

Use virus scanners

In order to detect and clean current viruses you must keep your
scanning tools up to date with the latest definition files.

Please see the following anti-virus vendor resources for more
information about the characteristics and removal techniques for the
malicious file known as ExploreZip.
"... hitting that right note, the right way, at the right time, is like
making love. Or touching the foot of God. Or maybe both."
- Carlos Santana

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