Lecture in Varna (Bulgaria, September 1994), on the symposium "Computing in Nuclear Physics"
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This is text of the lecture in Varna (Bulgaria, September 1994),
on the symposium "Computing in Nuclear Physics"


Dmitry Yu. Mostovoy, Yury P. Lyashchenko

DialogueScience, Inc.,
ul. Vavilova 40, GSP-1, 117967, Moscow, Russia
E-mail: dmost@dials.msk.su , lyu@dials.msk.su


        A method of protecting against computer viruses is described
        that is based not the traditional accumulation of data about
        potentially infinite number of new viruses but on storing
        information on a finite number of existing files in a computer.
        This method, by directly addressing BIOS for gaining access to
        the hard disk, guarantees reliable protection against virus


The anti-virus packages popular in the West like Microsoft Anti-Virus
and Norton Anti-Virus resemble each other in composition, functions,
and capabilities. They are polyphages with an external database
containing information about three to four thousand known viruses.
They may additionally include a resident sentry and a simple disk
inspector to check the CRC of files.

Why is this particular trend dominating the design of anti-virus
programs in the West? A few years back in the early stages of the
development of anti-virus tools, this strategy proved quite effective
and thus gained a strong foothold in the anti-virus market.
Nonetheless, a few viruses like Dark Avenger, Black Friday, Falling 
letters, etc, whose names clearly suggest their malicious 
activities, caused havoc all over the computer world.

But now the virus situation has changed radically. Thanks to modern
infection recovery software tools and to the user's deeper knowledge,
no computer virus is today allowed to flare up on a world-wide scale;
some virus or a group of related viruses may proliferate within the
confines of an institution, city, region or a country. Such local
epidemics are as a rule easily diagnosed and suppressed immediately.
But sustained intellectual efforts are needed to fight against these
epidemics which cause immense financial losses. Conventional anti-virus
utilities, even if they are capable of recognizing a large number of
various types of viruses, loose their efficacy and become less
reliable under the present virus situation. At present, anti-virus
programs are available for about 4000 concrete infectors but computer
viruses are being released almost every other day. A user, when the
4001-st virus invades his computer, is helpless to combat the saboteur
with the conventional software aids.

Furthermore, the policy "to every viral stain, a concrete
antivirus body" is generally expected to be slated to meet a dead end,
certainly not because of the drawbacks inherent in the design of
anti-virus programs. An anti-virus routine may contain the description
of viruses as an internal module or as an external database which it
references. In either case, anti-virus program is size limited, whereas
viruses may grow in number unboundedly.

Side by side with the ever-increasing number of simple 
infectors (the so-called student viruses), complex stealth 
viruses based on elegant hiding algorithms are also designed and 
proliferated. Only an anti-virus software that goes deep into the 
operating system to the BIOS level can detect them.

Additionally, polymorphic viruses do not contain any characteristic 
blocks in their codes, and therefore their detection requires the 
construction of complicated recognition algorithms based on processor 
emulation.  But such algorithms will perceptibly slow down the 
operation of anti-virus programs.

In Russia in particular and in former Soviet republics in general,
computer virus is really a national calamity from intellectual, moral,
social and material standpoints and has assumed formidable dimensions.
Intellectually it is a defeat because it is a challenge to
conscientious programmers, morally it is a misfortune because the
State has so far not safeguarded its citizens against this evil by
adequate legislation, socially it is a vice because the society has
not provided enough opportunities for the young talented programmers
to tap their skill and knowledge to useful purposes and materially it
is a disaster for the havoc it causes to national economy.  Well, 
these factors together with easy accessibility to modern computing 
systems, all contributed to the so-called Russian virus explosion. 
Its stray splinters can be tracked in the West, too. This naturally 
stimulated intensive search for new methods and techniques to 
counteract the hazard.


Therefore our company diverted our efforts in searching an entirely
new anti-virus technology for the problem: the result was the birth of
Advanced Diskinfoscope (ADinf) - a powerful diagnostic tool for
x-raying computer disks and diskettes at BIOS level. Organizing a
compact database containing information about finite number of files
in each particular drive is evidently a much better reliable
prevention method than storing data on all potentially infinite number
of viruses.

ADinf is a breakthrough in anti-virus technology as it deploys, unlike
in the conventional packages mentioned above, a basically new strategy
- its data integrity checker searches for viruses by keeping a close
watch over the changes taking place in a disk. Moreover, it scans a
disk, reading the data, sector by sector, directly via BIOS without
the assistance of the operating system. Such a search reveals every
virus known or unknown, polymorphic or stealth.

At the first start, ADinf retrieves full information on the master
boot record of a disk, boot sectors of logical drives, addresses of
bad clusters, directory tree structure, file information including
size, time and date of creation, and CRC. In subsequent sessions, 
ADinf checks the integrity of these data by collation and reports all 
changes that have taken place since the last session, paying special
attention to those changes which it suspects to be the result of virus
activity. On detecting such changes, it immediately generates an
on-screen warning message. Any change in file size or CRC without any
alteration in file creation time and date, or change in file creation
time showing a figure greater than 58 in seconds or a file date
greater than the current date are expertized by ADinf as induced by
virus activity. ADinf can keep strict watch over a user-specified
list of UNCHANGEABLE files and warns about any change, however minor
it may be, in such files. Its scan report gives full information about
newly created and deleted subdirectories, newly created, deleted,
moved, renamed files, newly appeared bad clusters, integrity of boot
sectors and other vital areas. It locks up all sites easily liable to
virus injection.

This philosophy has been partly realized by several software
designers, for example, McAfee Associates in Sentry, Symantec
Corporation in Norton Anti-Virus, Central Point Corporation in
Microsoft Anti-Virus and others. But they all have a common demerit in
that they do not utilize these checkers to full capacity. They detect
only the changes in files but fail to notice such operations as the
creation of new files, renaming of files, movement of files from one
directory to another, creation and deletion of directories, changes in
boot sectors and the master boot record. Virulent viruses may be
designed and are being designed precisely on these operations. Second,
these anti-virus packages keep control over a fixed set of files. If
certain files are deleted or new files are created, the disk
information tables in them need to be recompiled - and this is rather
inconvenient to the user. The most important drawback is that they
check a disk by reading through the operating system. Though there is
an "anti-stealth" option in them, modern stealth viruses hiding at Int
13h or disk controller, easily dodge detection by these packages.

Such a rigorous disk control in ADinf should seemingly be
time-consuming and inconvenient to the user. But ADinf is surprisingly
fast as it reads the sectors, accessing a disk via BIOS without the
assistance of DOS, thereby leaving no peepholes for stealth viruses.
In just 30 seconds it scans a 200Mb disk in a 486/33 system, while Dr
Solomon requires 45 seconds and Microsoft Anti-Virus three minutes to
complete its checks. The Diskinfo tables, which ADinf creates for its 
internal use, take about 40Kb disk space. Advanced DinkinfoScope
provides a comprehensive system of menu options to meet the exacting 
preferences and taste of any connoisseur user. It accepts a 
user-defined list of filename extensions of files to be taken under 
its control, skips the directories, from its checks when told, where 
files are subject to constant changes. Its originality and 
indispensability are readily apparent in its customizability, instant 
checks, expertise and high prediction reliability.

ADinf program incorporates a unique algorithm that has no parallel in
any other anti-virus tool, namely, the routine which searches for
stealth viruses utilizing their dodging capabilities. Strangely, the
hiding tactics is the weakest link in the dodging code that betrays a
stealth virus. It suffices to compare the file information generated
by DOS with the actual disk information: a discrepancy between them
confidently predicts the presence of stealth stains in a machine. In
other words, the ability of a virus to mask itself unmasks its
presence! Thus, generation of disk information at the BIOS level
opened a way for designing such comparison algorithms.

ADinf detects infection in time and thus assists in localizing virus
epidemics. What, if a virus, even a boot infector, infiltrates a
computer? ADinf instantly reinstates the original boot sector from the
image it holds in its tables and thus recovers a system from disaster.
This operation is conducted at the BIOS level followed by immediate
system rebooting in order to prevent reinfection. If it is a file
infector, ADinf Cure Module - the curing companion to ADinf - easily
restores the file to its original shape in toto.


ADinf Cure Module easily recovers infected files, without knowing the
format and behavior of a virus, i.e., it is a universal tool designed
to combat the strategies and tactics deployed by modern file infectors
and thus to aid in arresting local epidemics.

The principle underlying ADinf Cure Module is simple and
straightforward. Despite the multifarious diversity of viruses and
their modifications, paradoxically, there are only a few paths by
which a virus is injected into a file. This is the basic strategy of
ADinf Cure Module. In its daily scanning sessions, ADinf informs ADinf
Cure Module about the changes, if any, in a file since the last check.
ADinf Cure Module immediately scrutinizes these files and stores their
new information in its tables for restoring them after a virus attack.
When a virus attaches itself to a file, ADinf at once detects the
changes and calls for the Cure Module which tries to reinstate the
original shape of an infected file by comparing its status before and
after an attack. If ADinf Cure Module reports that a file has been
restored successfully, it really means what it says.

Thus, an infected file is recovered by reinstating its original status
from the image of its structure stored in ADinf Cure tables.
Consequently, a knowledge as to which virus infected the file is not
mandatory. Tables containing the necessary information for recovering
files take about 300 Kb on a 200Mb drive.

ADinf Cure Module cannot cure a file for each and every virus but it
does cure a file for almost all viruses. The restoration performance
is 97%, even for as-yet-unknown viruses. ADinf withstood this
performance percentage in an efficacy test conducted with a large
collection of files infected with various viruses widespread in
Eastern Europe. This performance is undoubtedly quite impressive. Of
course, no package can claim 100% efficacy.

Disk inspectors are also not a panacea against computer viruses.  
Their main demerit is the need for running them daily so as to keep a 
record of the changes taking place in a disk. Although such a run 
takes about 30 - 40 seconds per day, majority of computer users 
prefer to follow the proverb "peasant crosses himself only when it 
thunders", and begin to look for anti-virus problems only when his 
computer goes mad.  In such cases, disk inspectors are helpless.  
But, if the user is far-sighted, then  a disk inspector with a curing 
module will provide ample safety of his machine.


Advanced Diskinfoscope, ADinf, and its curing module form the core of
the DialogueScience Anti-Virus kit designed on the technology described
above. Additionally, this Anti-virus kit also includes the polyphage
Virus Hunter, which is extremely popular in Russia under the name
Aidstest. Virus Hunter recognizes and eradicates the viruses that are
widespread in Russia, and is upgraded almost every other week.
Therefore, it is an essential tool as a preliminary check for the
software products from Russia. Since, among the Russian viruses there
are also unconventional infectors, Virus Hunter is unavoidable even if
the user has a universal tool like ADinf Cure Module at his disposal.
The only drawback is that Virus Hunter cannot recognize complex
polymorphic viruses.

The latest add-on to the DialogueScience Anti-Virus kit is a
new-generation polyphage Dr.Web. On the whole it functions very much
like the traditional polyphage Virus Hunter, namely, it recognizes
those viruses that are known to it by certain characteristic blocks in
the virus code. But, what is new in its technology is that owing to the
built-in emulator Dr.Web tracks down to the virus, even if the virus is
camouflaged by encoders, compressors and vaccines. Consequently, it
easily detects and kills complex polymorphic viruses. And built-in
heuristic scaner makes Dr.Web possible to detect unknown viruses in 80%

The DialogueScience Anti-Virus Kit also includes a resident sentry. But
it radically differs from the sentries in western anti-virus utilities
in that it is supported by a special card. Owing to this hardware
support, The DialogueScience Anti-Virus Kit guarantees almost cent
percent data integrity, security and protection against any virus. It
is the cheapest hard-&-software anti-virus protection system available
in the world's computer market today.


The DialogueScience Anti-Virus Kit is dominating in Russia and former
Soviet republics: registered users of the Kit or of any components 
run to several thousands, while unregistered users count in millions
due to software piracy prevalent in this region.


1. N. N. Bezrukov, Computer viruses, Nauka, Moscow, 1991 (in Russian).

2. N. N. Bezrukov, Handbook on Computer Virology.
   Ukrainskaya Sovetskaya Entsiklopediya, Kiev, 1991 (in Russian).

3. D. Yu. Mostovoy, Modern technologies of defence against viruses.
   MirPK, No. 8, 1993, Moscow (in Russian).

4. D. Yu. Mostovoy, A Method of Detecting and Eradicating Known and 
   Unknown Viruses. Security and Control of Information Technology in 
   Society / R.Sizer et al. (Editors). Elsevier Science B.V. 
   (North-Holland), 1994.

5. DialogueScience Anti-Virus Kit, User's Guide, Moscow, 1993.

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