Since no one responded, I'll just say I found that an interesting article, thanks for drawing our attention to it. The writer doesn't seem to have tried very hard, really (perhaps understandably if the Russian Mafia was going to become invovled...).
I have no doubt it is possible to build a nuclear weapon. It is not a simple process by any means - read Tom Clancy's "The Sum Of All Fears" for a readable account of the efforts and costs involved - but as the author of the article has realised it's not really necessary to build an atomic bomb. A few fertiliser bombs in some big shopping malls, packed cinemas, amusement parks and soon your terrorism job is done. This is not new but it has gained a lot of attention recently. Trouble is, there really isn't a defence against that sort of thing (see the transcript I posted from my dad for a fuller discussion).