CIAC report on Michelangelo virus...

Rob Harper Rob.Harper at CONVEX.CSC.FI
Fri Mar 6 05:47:17 EST 1992

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>From: karyn at cheetah.llnl.gov (Karyn Pichnarczyk)
>Newsgroups: comp.virus
>Subject: CIAC Bulletin C-15: Michelangelo Virus (PC)
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>Date: 7 Feb 92 23:44:12 GMT
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>Approved: krvw at sei.cmu.edu

                           NO RESTRICTIONS
              The Computer Incident Advisory Capability
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                         Information Bulletin

                Michelangelo Virus on MS DOS Computers

February 6, 1992, 1400 PDT                                   Number C-15
Name: Michelangelo virus
Platform: MS-DOS computers
Damage: On March 6 will destroy all files on infected disks and
        diskettes that are accessed.
Symptoms: CHKDSK reports "total bytes memory" 2048 bytes less than
Detection: DDI Data Physician Plus! v 3.0C, FPROT 2.01, other
        anti-viral packages updated since late September 1991
Eradication: DDI Data Physician Plus! v 3.0C, FPROT 2.01, other
        anti-viral packages updated since late September 1991
               Critical Facts about Michelangelo Virus

The Michelangelo virus, one of the most widespread viruses among MS
DOS systems, infects the Master Boot Record of hard disks and the boot
sector of floppy disks.  This virus will destroy infected disks on
March 6 (Michelangelo's birthday).  It infects very rapidly and
quietly, usually showing no indication of its presence until a virus
detection utility notes its existence.

Infection Mechanism

This virus is very similar to the Stoned family of viruses (see CIAC
Bulletin A-28 for a description of the Stoned virus).  When a
Michelangelo-infected diskette is placed in the A: drive and the
machine is booted, the virus is loaded into memory from the infected
floppy disk.  It then quickly infects the machine by moving the hard
disk's original boot sector to another location on the disk, and
installs itself as the boot sector.  From then on, any access to
another disk spreads the virus to that disk.  The disk which infects
the hard disk does NOT have to be a bootable system diskette to spread
the infection.  Also, all boot infector viruses, such as this one, do
NOT affect user files, therefore, a backup prior to eradication will
enable full recovery of all user data and programs.

Potential Damage

On March 6 of any year this virus will destroy all data on any disk
from which the machine is booted.  This occurs by overwriting hard
disk sectors 1-17, heads 0-3, tracks 0-255, or the entire diskette
with random characters, thus making recovery questionable at best.
Note that if your hard disk is partitioned and contains another
operating system, such as UNIX, in the area overwritten, that data
will be destroyed as well.  On all other days of the year this virus
lays dormant, merely copying itself to other disks.  The infection
mechanism of this virus may also cause read errors to occur upon some
high density (1.2 M) diskettes.

A problem can occur if a disk is infected by both the Michelangelo and
the Stoned viruses AT THE SAME TIME.  Both move the 'original' boot
sector to the same location on the disk, so when the second infection
occurs, the original clean boot sector is destroyed by being
overwritten by the first virus.  CIAC recommends a low-level format of
the disk if this double-infection occurs, although performing the
DOS SYS operation may repair a damaged diskette, and performing the
undocumented FDISK/MBR operation (in DOS 5.0 only) may repair a
damaged hard disk.

Detection and Eradication

Because the Michelangelo virus has been discovered relatively
recently, only anti-virus products updated since early autumn of 1991
will detect it.  If you suspect your PC has this virus and do not have
an updated version of a virus scanner, running CHKDSK will report a
"total bytes memory" value 2048 bytes less than expected.  For
example, a PC with 640 KBytes of memory will normally return a value
of 655,360 bytes, with Michelangelo that value would be 653,312.  Of
course, having less "total bytes memory" does not necessarily mean a
virus is resident on your machine, as some valid memory resident
programs can affect this value as well.

CIAC is aware of at least two publicized cases of this virus being
inadvertently distributed by vendors.  The vendors involved are
Leading Edge and DaVinci Systems; both vendors have made an attempt to
contact all recipients of the software involved.

CIAC stresses the importance of checking all incoming diskettes with
an anti-viral utility, such as VIRHUNT from DDI's Data Physician Plus!
package.  CIAC recommends that once a system has had a virus
eradicated, it be powered down.  The computer should then be observed
closely throughout the entire boot-up process.  Another virus scan
should be performed on the machine to ensure that it is devoid of any

For additional information or assistance, please contact CIAC:

Karyn Pichnarczyk
(510) 422-1779 or (FTS) 532-1779
karyn at cheetah.llnl.gov

(FAX) (510) 423-8002 or (FTS) 543-8002

Send e-mail to ciac at llnl.gov or call CIAC at

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incidents.  Some of the other teams include the NASA NSI response
team, DARPA's CERT/CC, NAVCIRT, and the Air Force response team.  Your
agency's team will coordinate with CIAC.

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