Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!spool.mu.edu!news.cs.indiana.edu!widener!netnews.upenn.edu!vax1.cc.lehigh.edu!cert.sei.cmu.edu!krvw
From: PJML@ibma.nerc-wallingford.ac.uk (Pete Lucas)
Newsgroups: comp.virus
Subject: Can such a virus be written .... (PC)
Message-ID: <0006.9106271453.AA02305@ubu.cert.sei.cmu.edu>
Date: 26 Jun 91 11:10:19 GMT
Article-I.D.: ubu.0006.9106271453.AA02305
Sender: Virus Discussion List <VIRUS-L@LEHIIBM1>
Lines: 16
Approved: krvw@sei.cmu.edu

Most DOS PCs do not implement a hardware 'media change' flag, so they
do not know that a diskette has been inserted until you try reading
from it.  (this is unlike an Apple Mac that has a 'media change' sense
on its diskette drive).
A virus doesnt 'know' that a new diskette has been inserted on a PC
until the virus has had a look at whats there. Of course the write-protect
notch/slide is 99.99% effective in my experience at preventing any
illicit writes; you would, of course, have write-protected any diskette
you put in the drive before doing the hypothetical DIR command, wouldnt
you?
(I do actually have a notchless diskette that on *some* drives can be
written to - the diskette jacket is semi-transparent and on drives
that use optical notch-sensing, enough light *sometimes* gets past to
make the thing writable....  oh confusion!)

          Pete Lucas PJML@UK.AC.NWL.IA    PJML%IA.NWL.AC.UK@UKACRL