Re: Was Cohen the first?

[iang@cs.berkeley.edu (Ian Goldberg)]

In article <199604070321.TAA02171@myriad>,
Matthew Ghio  <ghio@myriad.alias.net> wrote:
>Despite this, the Apple II never became a popular virus-writing platform.
>There are several possible reasons for this, but one of the main ones is
>that few Apple II users had hard disks.  On the IBM PC, it was easy for a
>virus to get on the hard disk, then systematically infect every floppy disk
>put into the system.  Apple II users, in contrast, often booted from
>floppies, and often rebooted when switching to a different software package,
>thus purging the virus from memory.  (Pressing control-reset on the Apple II
>keyboard would always pull the reset line on the CPU, so it wasn't possible
>to trap the interrupt like it is possible to trap ctrl-alt-del on the PC.)

Not true.  Pressing ctrl-reset jumped to the interrupt routine pointed
to by the vector at (I think) 1010/1011, if the contents of that vector
checksummed correctly with the contents of the next byte (1012), and
otherwise reset the computer.  It certainly was possible (and useful)
to trap ctrl-reset.  Also, even when a reset occurred, not all of the
memory was cleared, so you could in fact keep code in memory across
a reset, if you could arrange to have it run on the other side of the
boot.

As you pointed out, it was very easy to write viruses for the Apple ][.
The "slave" disk layout contained two blank sectors (.5 K) within the
DOS image that get loaded into memory.  The designers may as well have
labelled it "put virus here".

   - Ian "Been there; done that..."