[Coco] Re: Coco virus/worms are possible!

[David]

Would it be possible to use such an entry point (typing 'dir') to load code
that patches disk basic, so that future 'dirs' on other floppies -writes-
said code to the floppy, 'infecting' it? (this would of course only be in
effect after loading an infected disk, and before powering off, or
'resetting' basic)

is this possible?

----- Original Message -----
From: Charlie <chazbeenhad at hotmail.com>
To: <coco at maltedmedia.com>
Sent: Monday, December 13, 2004 10:48 PM
Subject: [Coco] Re: Coco virus/worms are possible!


> The Crystal City (Jeremy Spiller) by Gosub software. This game starts by
> entering DIR.
>
> Charlie
>
>
> "Arthur Flexser" <flexser at fiu.edu> wrote in message
> news:Pine.SOL.4.21.0412130104240.12181-100000 at solix.fiu.edu...
> > On Sun, 12 Dec 2004, Robert Gault wrote:
> >
> > > A topic that comes up occasionally is "can a Coco be infected in a
> > > manner similar to current PCs". Generally the answer is no but I've
just
> > > come across a method that could make infection a possibility.
> > >
> > > I was asked about a Coco game that was stated to start running when
the
> > > DIR command was issued. Now how can that be possible as DIR just
prints
> > > text to the screen. Well, DIR does much more in order to get that text
> > > for printing.
> > >
> > > One of the things done by DIR is to load the disk FAT table into a
> > > buffer at $600. As this table is no larger than a 256 byte sector,
this
> > > should be safe. However, the game formats track 17 with six 1024 byte
> > > sectors. That means when DIR loads T17S2 (the FAT) it gets more than
> > > bargained for. The buffer is flooded way past the NMI vector at $983.
> > >
> > > Since all disk I/O makes use of the NMI, this game probably puts an
> > > address into $982 that vectors to some code loaded from T17S2. Nothing
> > > really bad can happen on a floppy system but on a hard drive system a
> > > malicious program could erase the hard drive.
> > >
> > >
> >
> > This sounds like an urban legend to me, at least in the absence of
> information
> > about what game supposedly does this.  Steve Bjork wrote a CoCo virus of
> this
> > sort, he said, but never released it, just to see if it could be done.
> But it
> > seems highly unlikely to me that there would have been a game that used
> this
> > technique without anyone prior to just now having remarked upon it.
> >
> > Art
> >
> >
> >
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> >
>
>
>
>
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