From: eugene@kamis.msk.su (Eugene V. Kaspersky)
Newsgroups: comp.virus
Subject: MegaVirus as Re: On the definition of viruses
Date: 18 Jan 93 18:45:30 GMT

Hello!

Fred Cohen writes:

> Computer viruses do not have to be malicious, they do not have
> to be Trojan horses, and they do not have to enter without the
> knowledge or consent of the user. Any definition that depends on
> these properties depends on peoples' opinions, skills, and knowledge,
> and are thus not "testable" in the scientific sense of the word.

Yes, to set the virus definition it's a very difficult task. I think that
it is impossible to define the virus. A small example for beginning:

One my friend wrote a virus. It's a extremely primitive program that
contains several MS-DOS commands which are united into one BAT-file named
VIRUS.BAT.

echo  ---
echo  Hello! I'm the virus!
echo  Look at your watch. Waiting ...
pause
echo  Is today Friday, 13th ?
echo  If 'yes' please type FORMAT C: and say YES for all the questions.
echo         If it's not enough please drop your monitor and
echo         [...skiped...]
echo  If 'no' please copy this program to all your friends because
echo  this is a very useful program!
echo  ---

Several color effects were added to this BAT file also.
Is this a virus? No? One week after first execution of this program
about 100 computers were 'infected' by this ... program? ... virus? Those
are about a half of all the computers of the company where this gay works
now. The users like this program-joke and copy it. So this program
replicates very well, its name is VIRUS.BAT and it's a dangerous because it
say "FORMAT C:"  and 'good user' can do this. Is this not a virus?

Another one example: virus-packer.
This imaginary program stays resident and on running any not packed COM or
EXE files asks: "Do you wish to PACK your program? <Y/N>" and then packs
and appends itself to the packed file at 'Y' pressing. On execution
'infected' program types "I'm infected by VIRUS-PACK, do you wish to
remove me? <Y/N>" and then unpacks the file and removes its body on 'Y' or
stays memory resident on 'N'. Is this the virus-like utility only and not a
virus?


> So what is a computer virus? In simple terms, it is a sequence
> of instructions that, when interpreted in an appropriate environment,
> "replicates" in that at least one relica also "replicates", etc., ad
> infinitum.

The last condition is incorrect because there are the viruses which
replicates a limited times. I forgot the name of example but this virus
contains the 'generation counter' and it not replicates on N generation. So
the condition must be as: "it 'replicates' at least several (more than 1)
times, on other cases this is a Trojan horse installator".


> Want an example? A backup program replicates by making an
> exact copy of itself (if it does a good job) on the backup media.  In

It's a bad example. MS-DOS, PC-DOS (I operate the IBM-PC terms only, sorry)
are the viruses also:

- - they replicate:
 SYS A:
 COPY *.* A:

- - they are very dangerous (I found one MS-DOS security option only, this is
two FAT copies);

- - they load itself silently and without user consent.

MS-DOS is a virus! That is a shock for antiviral researchers and vendors!
It's need to update all the antiviral databases.


So I'll try to set several virus definitions.

DEF_1: The virus
> is a sequence
> of instructions that, when interpreted in an appropriate environment,
> "replicates" in that at least one relica also
The virus is useless program *and* it can't restore the infected object and
remove itself by 'DOS prompt' way.

But this definition is bad also.
There are several question: that is 'useless program' ?
The virus packer is useful virus. That is 'remove itself by ... ' ?
Could somebody extend this way of virus definition?


And who say that the virus is 'a sequence of instructions'? The real
virus can consists of several parts of code, a *sequences* of instructions
i.e. several different files, sectors, RAM areas. Well, let this virus
named as 'multipartite virus'.

So, the MS-DOS is useful programs, but the MS-DOS floppy with specific
AUTOEXEC.BAT is a multipartite-virus:

AUTOEXEC.BAT:

   sys a:
   copy *.* a:\
   sys b:
   copy *.* b:\
   ...
   sys z:
   copy *.* z:\

This MP-virus (multipartite virus) infects all the accessible logical disks
very well.

Well, lets examine all the sequences of instructions of all the computers.
This multitude of files, sectors, RAMs is one great MP-virus (it's very
dangerous and it can replicate). So,

DEF_2: All the programs of all the computers are the parts of the World
MegaVirus.


DEF_3: It's impossible to set the virus definition.

It's because the viruses are manufactured by men and the virus definitions
are produced by men also. So if we say new virus definition there are
someone who can write the counter-example virus. As the result the true
virus definition is DEF_2 only.

:-)


Last note:

> I'm really glad that I no longer sell virus defenses, because I think it's
> a pretty shady business (except for a few good companies that tell the
> truth about viruses and their products).

It's a good statement but it's limited. It's better to say

To sell [anything]
> it's a pretty shady business (except for a few good companies that tell the
> truth about
[skipped]
> their products).


Best regards,

Eugene
- -- 
- --  Eugene Kaspersky, KAMI Group, Moscow, Russia  
- --  eugene@kamis.msk.su, +7 (095) 499-1500