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Article #4347

Generic detection of Boot Sector/MBR viruses (was Re: Is this a real virus?) (PC)

#4347
From: McAfee Associates
Date: Wed, 16 Dec 1992 19:24
34 lines
2220 bytes
Good morning Vesselin,

You wrote:
>Ah, this explains the "Generic Boot Virus" report... It seems to me
>that SCAN is using some kind of heuristics (Aryeh?) and reports a
>"generic" boot (or partition) virus each time when something seems
>wrong with the boot sector(s) - like missing names of the hidden DOS
>files, missing signature (0AA55h), etc. In your case the whole
>contents of the boot sector has been destroyed, so its contents has
>become obviously "abnormal". This has triggered SCAN's heuristics
>(just a wild guess; I'm not certain that it is indeed so).

The Generic Boot Sector and Master Boot Record (partition table) virus
detection routines are actually looking for several common instructions 
that appear over and over again in different viruses such as Stoned, 
Joshi, and so forth.  By looking for these, we can detect variants/new
viruses based on older viruses.

The Generic Boot Sector/MBR code is not doing a "fitness check" to see
if the partition table (the actual data) or 55 AA signature is valid,
since those would not neccessarily be due to a virus infection (e.g.,
could be an unformatted drive).  Likewise, we don't do a filename check
since that could cause false positives with non-DOS operating systems 
such as Unix and OS/2.

Regards,

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From: mcafee@netcom.com (McAfee Associates)
Newsgroups: comp.virus
Subject: Generic detection of Boot Sector/MBR viruses (was Re: Is this a real virus?) (PC)
Message-ID: <0003.9212181845.AA00632@barnabas.cert.org>
Date: 16 Dec 92 19:24:03 GMT
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