The Guardian has the story.
Here's the important bit:
Blueprints for a sophisticated and compact nuclear warhead have been found in the computers of the world's most notorious nuclear-smuggling racket, according to a leading US researcher.
David Albright, a physicist, former UN weapons inspector and authority on the nuclear smuggling ring run by the Pakistani metallurgist Abdul Qadeer Khan, said the "construction plans" included previously undisclosed designs for a compact warhead that could fit on Iran's medium-range ballistic missiles.
"These advanced nuclear weapons designs may have long ago been sold off to some of the most treacherous regimes in the world," wrote Albright.