The increasing success in shutting down Iran arms smuggling efforts is mainly due to good intelligence work. For example, a known (to U.S. investigators) arms smuggler, Iranian citizen Amir Hossein Ardebili, was traced to the Caucasus (Georgia) two years ago, arrested by local police and transported to the United States. This was kept quiet, because Ardebili's laptop was also captured, and proved to be full of useful information. This persuaded Ardebili to flip and plead guilty a year after his arrest. Ardebili had been tracked since 2004, so the U.S. already had a thick file on him. With his arms smuggling career in tatters, it appears that Ardebili provided information that was not on his computer.
Like his initial arrest (and the prior three years of pursuit), the after effects of Ardebili's capture will not be known for some time. It was only recently that the U.S. government released information on Ardebili's arrest and prosecution. There are apparently many more such cases underway.
Ever since the U.S. embargo was imposed in 1979 (after Iran broke diplomatic protocol by seizing the American embassy), Iran has sought, with some success, to offer big money to smugglers who can beat the embargo and get needed industrial and military equipment. This is a risky business, and American and European prisons are full of Iranians, and other nationals, who tried, and often failed, to procure forbidden goods. The smuggling operations are currently under more scrutiny, and attack, because of Iran's growing nuclear weapons program. But the Iranians simply offer more money, and more smugglers step up to keep the goodies coming.