In message , at 20:07:27 on Mon,
26 Feb 2007, Graeme Wall remarked:

A dirty bomb is a conventional explosive device designed to spread
radioactive 'shrapnel' around, any biological component would be killed by
the radioactivity long before delivery.

Not quite. It's a conventional explosive device designed to spread
*biological* 'shrapnel' around. It doesn't have to be a very big bang,
either. Just enough to do the spreading. And nothing radioactive
involved at all.
--
Roland Perry