That's the case of North Korea.
Russia also is a supporter of Iran going nuclear, WHY????
Russian nuclear industry presses for new contracts - they want money. And probably, they can't afford not having it - not many customers.
Russia actualy doesn't build a bomb for Iran - but it seeks to be a successful mediator -> authority in Aran world -> influence.
Russia build a light water reactor - not helping Iran to enrich fissile materials to the weapons grade.
Iran's technology is from Pakistan which is an US's ally. Russia also is selling arms to the wild eyed oil dictator of Venezuela.
Venezuela doesn't threaten Russia and it offers money. A pity we have a shortage of Saiga shotguns for public because of Chavez's order. Also not many customers for arms - Russian military orders nothing.
It really depends on how much money one has. The nuclear and arms industry of Russia really have little options.
Anyway, we have capitalism now. "Any substantial fortune was got in a criminal way" - Karl Marx.