But what if the page uses HTML5 audio to "jump the gap" and reprogram all nearby electronic devices to attack you on 1/1/2014!?

Obviously, VM should have no access to audio outputs, display driver should be rewritten to scramble output to be only viewable using a Lenslok-like device and the whole setup should run on a isolated computer staying in a clean room with a dead-man switch installed that - in case of unforeseen consequences - would quickly power a whole apartment down and call for emergency.

I think you're neglecting to consider the possibility of seismic communication by doing a lot of client-side computation to make the CPU fan kick on and off.

Dust of your trusty C64, then you have plenty of time to get yourself some coffee and pull the plug, before the audio starts to play.

Im surprised so many have taken this comment seriously.

not positively surprisrd, more like dissapoined.

That's professional paranoia right there. Someone give this man a job and a hard hat.

A tin-foil hat would probably be better off for his situation.

It prevents mind reading.