Destroying a computer via software

[bruce@pixar.com (Bruce Perens)]

>>>>> "Rob" == Rob Browning <osiris@cs.utexas.edu> writes:
Rob> Well, I'd like to see the code for the infinite loop that'd melt
Rob> down my processor.  I've written a few in my time (accidentally),
Rob> and the machine's still here.

From: Christian Lynbech <lynbech@daimi.aau.dk>
> The issue of destroying a computer through software was once (probably
> has been several times) discussed on alt.folklore.computers. 
> It is (or rather was) possible, but only in one known case. I do not
> remember many details, but some old microcomputer (Commodore of some
> sort I believe) allowed you to flip a bit in a register on the video
> chip that would cause power to build up somewhere until the chip
> eventually died.

It is possible to destroy a number of existing PC and PC-clone video
monitors by programming the VGA video timing registers. This is why we
try to be careful not to allow people to set their video card to just
any timing. I think that most of the susceptible monitors are out of
circulation, but of course there's lots of legacy hardware running Debian.

The monitors with this problem drive the flyback transformer at the
horizontal sync frequency. They have a sync detector that shuts down
the transformer if sync is absent, but this sync detector does not shut
down the transformer if it sees a very low horizontal frequency, or
only vertical sync without horizontal sync. The transformer gets driven
with only vertical sync or with very low frequency horizontal sync.
This causes the primary winding to have too low an impedance, which
causes too much current to flow through it, and it burns up.

The original IBM CGA color monitor is said to have this problem, and many
clones of it were said to have it as well. I don't know about more modern
hardware. If you have a monitor that is susceptible to this, it is possible
to destroy it by typing the wrong numbers into your XFree86 configuration
file.

This has been discussed in boring detail on various public forums. All of
the details are available to any malicious person. Thus, it's best for
everyone to know about the vulnerability.

	Thanks

	Bruce