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

[Charlie]

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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