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CA-2004-02 Email-borne Viruses


CERT Advisory CA-2004-02 Email-borne Viruses

Original release date: January 27, 2004
Last revised: --
Source: CERT/CC

A complete revision history can be found at the end of this file.

Systems Affected

* Any system running Microsoft Windows (all versions from Windows 95
and up) and used for reading email or accessing peer-to-peer file
sharing services.


In recent weeks there have been several mass-mailing viruses released
on the Internet. It is important for users to understand the risks
posed by these pieces of malicious code and the steps necessary to
protect their systems from virus infection.

I. Description

Over the past week, we have seen two more mass-mailing viruses,
W32/Bagle and W32/Novarg, impact a significant number of home users
and sites. The technology used in these viruses is not significantly
different from prior mass-mailing viruses such as W32/Sobig and
W32/Mimail. Unsolicited email messages containing attachments are sent
to unsuspecting recipients. They may contain a return address, a
provocative envelope, or something else that encourages its receiver
to open it. This technique is called social engineering. Because we
are trusting and curious, social engineering is often effective. The
widespread impact of these latest viruses, which rely on human
intervention to spread, demonstrates the effectiveness of social

It continues to be important to ensure that anti-virus software is
used and updated regularly, that attachments are examined on mail
servers, and that firewalls filter unneeded ports and protocols. It
also remains necessary that users be educated about the dangers of
opening attachments, especially executable attachments.

CERT Incident Note IN-2004-01 - W32/Novarg

CERT Incident Note IN-2003-03 - W32/Sobig.F

CERT Incident Note IN-2003-02 - W32/Mimail

II. Impact

A virus infection can have significant consquences on your computer
system. These consequences include, but are not limited to:

* Information disclosure - Mass-mailing viruses typically harvest
email addresses from the addressbooks or files found on an
infected system. Some viruses will also attempt to send files from
an infected host to other potential victims or even back to the
virus author. These files may contain sensitive information.

* Add/Modify/Delete files - Once a system is compromised, a virus
could potentially add, modify or delete arbitrary files on the
system. These files may contain personal information or be
required for the proper operation of the computer system.

* Affect system stability - Viruses can consume significant amounts
of computer resources causing a system to run slowly or be
rendered unusable.

* Install a backdoor - Many viruses will install a backdoor on an
infected system. This backdoor may be used by a remote attacker to
gain access to the system, or view/add/modify/delete files on the
system. These backdoors may also be leveraged to download and
control additional tools for use in distributed denial-of-service
(DDoS) attacks against other sites.

* Attack other systems - Systems infected by viruses are frequently
used to attack other systems. These attacks frequently involve
attempts to exploit vulnerabilities on the remote systems or
denial-of-service attacks that utilize a high volume of network

* Send unsolicited bulk email (spam) to other users - There have
been numerous reports of spammers leveraging compromised systems
to send unsolicited bulk email. Frequently these compromised
systems are poorly protected end user computers (e.g., home and
small business systems).

III. Solution

In addition to following the steps outlined in this section, the
CERT/CC encourages home users to review the "Home Network Security"
and "Home Computer Security" documents.

Home Network Security

Home Computer Security

Run and maintain an anti-virus product

While an up-to-date antivirus software package cannot protect against
all malicious code, for most users it remains the best first line of
defense against malicious code attacks. Users may wish to read
IN-2003-01 for more information on anti-virus software and security

CERT Incident Note IN-2003-01

Most antivirus software vendors release frequently updated
information, tools, or virus databases to help detect and recover from
malicious code. Therefore, it is important that users keep their
antivirus software up to date. The CERT/CC maintains a partial list of
antivirus vendors.

Computer Virus Resources

Many antivirus packages support automatic updates of virus
definitions. The CERT/CC recommends using these automatic updates when

Do not run programs of unknown origin

Do not download, install, or run a program unless you know it to be
authored by a person or company that you trust.

Email users should be wary of unexpected attachments. Be sure you know
the source of an attachment before opening it. Also remember that it
is not enough that the mail originated from an email address you
recognize. The Melissa virus spread precisely because it originated
from a familiar email address.

Users should also be wary of URLs in email messages. URLs can link to
malicious content that in some cases may be executed without user
intervention. A common social engineering technique known as
"phishing" uses misleading URLs to entice users to visit malicious web
sites. These sites spoof legitimate web sites to solicit sensitive
information such as passwords or account numbers.

In addition, users of Internet Relay Chat (IRC), Instant Messaging
(IM), and file-sharing services should be particularly careful of
following links or running software sent to them by other users. These
are commonly used methods among intruders attempting to build networks
of distributed denial-of-service (DDoS) agents.

Use a personal firewall

A personal firewall will not necessarily protect your system from an
email-borne virus, but a properly configured personal firewall may
prevent the virus from downloading additional components or launching
attacks against other systems. Unfortunately, once on a system, a
virus may be able to disable a software firewall, thus eliminating its

Email gateway filtering

Depending on your business requirements, it is advisable to configure
filtering of specific file extensions of email attachments at the
email gateway. This filtering should be configured carefully, as this
may affect legitimate attachments as well. It is recommended that
attachments are quarantined for later examination and/or possible

Recovering from a system compromise

If you believe a system under your administrative control has been
compromised, please follow the steps outlined in

Steps for Recovering from a UNIX or NT System Compromise

Authors: Jeff Carpenter, Chad Dougherty, Jeff Havrilla, Allen
Householder, Brian King, Marty Lindner, Art Manion, Damon Morda, Rob

This document is available from:

CERT/CC Contact Information

Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890

CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) /
EDT(GMT-4) Monday through Friday; they are on call for emergencies
during other hours, on U.S. holidays, and on weekends.

Using encryption

We strongly urge you to encrypt sensitive information sent by email.
Our public PGP key is available from

If you prefer to use DES, please call the CERT hotline for more

Getting security information

CERT publications and other security information are available from
our web site

To subscribe to the CERT mailing list for advisories and bulletins,
send email to Please include in the body of your

subscribe cert-advisory

* "CERT" and "CERT Coordination Center" are registered in the U.S.
Patent and Trademark Office.

Any material furnished by Carnegie Mellon University and the Software
Engineering Institute is furnished on an "as is" basis. Carnegie
Mellon University makes no warranties of any kind, either expressed or
implied as to any matter including, but not limited to, warranty of
fitness for a particular purpose or merchantability, exclusivity or
results obtained from use of the material. Carnegie Mellon University
does not make any warranty of any kind with respect to freedom from
patent, trademark, or copyright infringement.

Conditions for use, disclaimers, and sponsorship information

Copyright 2004 Carnegie Mellon University.

Revision History
January 27, 2004: Initial release

Version: PGP 6.5.8


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