||Home : Advisories : Melissa Macro Virus|
||Melissa Macro Virus
||27th March 1999
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CERT Advisory CA-99-04-Melissa-Macro-Virus
Original issue date: Saturday March 27 1999
Last Revised: Saturday March 27, 1999
* Machines with Microsoft Word 97 or Word 2000
* Any mail handling system could experience performance problems or
a denial of service as a result of the propagation of this macro
At approximately 2:00 PM GMT-5 on Friday March 26 1999 we began
receiving reports of a Microsoft Word 97 and Word 2000 macro virus
which is propagating via email attachments. The number and variety of
reports we have received indicate that this is a widespread attack
affecting a variety of sites.
Our analysis of this macro virus indicates that human action (in the
form of a user opening an infected Word document) is required for this
virus to propagate. It is possible that under some mailer
configurations, a user might automatically open an infected document
received in the form of an email attachment. This macro virus is not
known to exploit any new vulnerabilities. While the primary transport
mechanism of this virus is via email, any way of transferring files
can also propagate the virus.
Anti-virus software vendors have called this macro virus the Melissa
macro or W97M_Melissa virus.
The Melissa macro virus propagates in the form of an email message
containing an infected Word document as an attachment. The transport
message has most frequently been reported to contain the following
Subject: Important Message From
Where is the full name of the user sending the message.
The body of the message is a multipart MIME message containing two
sections. The first section of the message (Content-Type: text/plain)
contains the following text.
Here is that document you asked for ... don't show anyone else ;-)
The next section (Content-Type: application/msword) was initially
reported to be a document called "list.doc". This document contains
references to pornographic web sites. As this macro virus spreads we
are likely to see documents with other names. In fact, under certain
conditions the virus may generate attachments with documents created
by the victim.
When a user opens an infected .doc file with Microsoft Word97 or
Word2000, the macro virus is immediately executed if macros are
Upon execution, the virus first lowers the macro security settings to
permit all macros to run when documents are opened in the future.
Therefore, the user will not be notified when the virus is executed in
The macro then checks to see if the registry key
has a value of "... by Kwyjibo". If that registry key does not exist
or does not have a value of "... by Kwyjibo", the virus proceeds to
propagate itself by sending an email message in the format described
above to the first 50 entries in every MAPI address book readable by
the user executing the macro. Keep in mind that if any of these email
addresses are mailing lists, the message will be delivered to everyone
on the mailing lists. In order to successfully propagate, the affected
machine must have Microsoft Outlook installed; however, Outlook does
not need to be the mailer used to read the message.
Next, the macro virus sets the value of the registry key to "... by
Kwyjibo". Setting this registry key causes the virus to only propagate
once per session. If the registry key does not persist through
sessions, the virus will propagate as described above once per every
session when a user opens an infected document. If the registry key
persists through sessions, the virus will no longer attempt to
propagate even if the affected user opens an infected document.
The macro then infects the Normal.dot template file. By default, all
Word documents utilize the Normal.dot template; thus, any newly
created Word document will be infected. Because unpatched versions of
Word97 may trust macros in templates the virus may execute without
warning. For more information please see:
Finally, if the minute of the hour matches the day of the month at
this point, the macro inserts into the current document the message
"Twenty-two points, plus triple-word-score, plus fifty points for
using all my letters. Game's over. I'm outta here."
Note that if you open an infected document with macros disabled and
look at the list of macros in this document, neither Word97 nor
Word2000 list the macro. The code is actually VBA (Visual Basic for
Applications) code associated with the "document.open" method. You can
see the code by going into the Visual Basic editor.
If you receive one of these messages, keep in mind that the message
came from someone who is affected by this virus and they are not
necessarily targeting you. We encourage you to contact any users from
which you have received such a message. Also, we are interested in
understanding the scope of this activity; therefore, we would
appreciate if you would report any instance of this activity to us
according to our Incident Reporting Guidelines document available at:
* Users who open an infected document in Word97 or Word2000 with
macros enabled will infect the Normal.dot template causing any
documents referencing this template to be infected with this macro
virus. If the infected document is opened by another user, the
document, including the macro virus, will propagate. Note that
this could cause the user's document to be propagated instead of
the original document, and thereby leak sensitive information.
* Indirectly, this virus could cause a denial of service on mail
servers. Many large sites have reported performance problems with
their mail servers as a result of the propagation of this virus.
* Block messages with the signature of this virus at your mail transfer
Nick Christenson of sendmail.com provided information about
configuring sendmail to filter out messages that may contain the
Melissa virus. This information is available from the follow URL:
* Utilize virus scanners
Most virus scanning tools will detect and clean macro viruses. In
order to detect and clean current viruses you must keep your
scanning tools up to date with the latest definition files.
+ McAfee / Network Associates
+ Trend Micro
* Encourage users at your site to disable macros in Microsoft Word
Notify all of your users of the problem and encourage them to
disable macros in Word. You may also wish to encourage users to
disable macros in any product that contains a macro language as
this sort of problem is not limited to Microsoft Word.
In Word97 you can disable automatic macro execution (click
Tools/Options/General then turn on the 'Macro virus protection'
checkbox). In Word2000 macro execution is controlled by a security
level variable similar to Internet Explorer (click on
Tools/Macro/Security and choose High, Medium, or Low). In that
case, 'High' silently ignores the VBA code, Medium prompts in the
way Word97 does to let you enable or disable the VBA code, and
'Low' just runs it.
Word2000 supports Authenticode on the VB code. In the 'High'
setting you can specify sites that you trust and code from those
sites will run.
* General protection from Word Macro Viruses
For information about macro viruses in general, we encourage you
to review the document "Free Macro AntiVirus Techniques" by Chengi
Jimmy Kuo which is available at.
We would like to thank Jimmy Kuo of Network Associates, Eric Allman
and Nick Christenson of sendmail.com, Dan Schrader of Trend Micro, and
Jason Garms and Karan Khanna of Microsoft for providing information
used in this advisory.
Additionally we would like to thank the many sites who reported this
This document is available from:
CERT/CC Contact Information
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
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Our public PGP key is available from http://www.cert.org/CERT_PGP.key.
If you prefer to use DES, please call the CERT hotline for more
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