From: bontchev@fbihh.informatik.uni-hamburg.de (Vesselin Bontchev)
Newsgroups: comp.virus
Subject: Re: Filler virus (PC)
Date: 11 Dec 92 17:44:46 GMT

mcafee@netcom.com (McAfee Associates) writes:

> Considering that the other anti-viral program appeared several years
> after VIRUSCAN was released, I think it is fair to say that SCAN does
> not contain a "shoddy scan string,"

I disagree. It absolutely doesn't matter when the anti-virus program
has been released. What does matter is (1) when the program has been
updated to detect this virus, (2) when did the virus appear, and (3)
are there any other possible scan strings for that virus.

If a virus like Cascade appears tomorrow, and if it uses variable
encryption, so that the only possible scan string is the (short)
decryptor in the beginning, guess what will both McAfee Associates and
any other anti-virus company pick as a scan string...

> rather, (1) the other program was 
> not adequately tested against existing anti-viral programs for 
> compatibility problems before release; (2) the other program does not
> cipher its virus search strings, opening the possibility of false alarms
> with other anti-viral programs which use the same search strings, and

Now, -that- is definitively fair to say. Any scanner-like anti-virus
program that doesn't do the above (and that doesn't clean up the
memory after itself upon termination) is plain silly.

> (3) this problem is not adequately documented in the other programs'
> documentation.

Well, in this particular case, it is documented... :-) They just tell
you in the docs that their program is incompatible with any other
anti-virus software... :-))

> In one of my chats with the other programs' technical support staff, I
> was told that the problem should be fixed in the new version of their 
> software.  Hopefully, this problem will disappear as users upgrade to 
> the current version of the program.

[rumors mode ON]

Allegedly, a version of the product mentioned will be included in
MS-DOS 6.0. Allegedly, this particular problem has been already fixed
in that particular version.

[rumors mode OFF]

> When a new anti-viral program is brought to market, who should be
> responsible for compatibility-testing it to ensure that no false
> alarms exist with existing programs?  And to what extent should
> testing be done?  And who should be responsible for fixing any
> incompatibilities?  Comments, anyone? <G>

That's a really good idea... As Dr. Solomon says, it's very easy to
create the perfect virus detector. It will achieve 100% detection rate
when tested with -any- virus collection. It can be just a short .BAT
file. Here it is:

echo %1 is a virus.

(or something similar, to include the boot sectors testing, but you
get the idea).

Unfortunately, such program has no practical use, since it gives an
infinite number of false positives. The tough problem is to create a
scanner that still has a good enough detection rate, but has no false
positives...

Unfortunately, there is no simple way to test a scanner for false
positives... False negatives are easy - you just get a huge virus
collection and count how many viruses the scanner -doesn't- detect...
I really don't know how a reliable false positive test should be
performed... One idea is to get all the MS-DOS software from Simtel20
(it is available on CD-ROM), unpack it and run the scanners on all the
executable files. Another idea is to run each scanner on a wide range
of other anti-virus programs, maybe even including itself. At the
VTC-Hamburg we are working on a test protocol about how anti-virus
tests should be performed, so any ideas are welcome.

Regards,
Vesselin
- -- 
Vesselin Vladimirov Bontchev          Virus Test Center, University of Hamburg
Tel.:+49-40-54715-224, Fax: +49-40-54715-226      Fachbereich Informatik - AGN
< PGP 2.0 public key available on request. > Vogt-Koelln-Strasse 30, rm. 107 C
e-mail: bontchev@fbihh.informatik.uni-hamburg.de    D-2000 Hamburg 54, Germany