TOKYO -- Their bags crammed with shiny new electronic goods, the passengers on the battered North Korean ferry looked like any other tourists returning from a shopping trip in the malls of Tokyo.
But the PlayStations and other gadgets carried onto the Mangyongbong-92 ferry ended up not as children's gifts but as components in Pyongyang's military hardware.
Japanese officials said North Korean spies have trawled electronic retail outlets in Tokyo for many years as part of a covert operation to exploit their neighbor's technological know-how.
Seemingly innocent consumer goods, including games consoles and camera lenses, were openly carried out of the country to the communist regime, their components finding their way into missiles now aimed back at Japan.
Suspicions that the ferry was being used as a conduit for a military trade in electronics, as well as a smuggling route for amphetamines and counterfeit cash, have long been held in Japan.
Although the accusations have been dismissed as lies by Pyongyang, Tokyo banned the Mangyongbong-92 from Japanese waters for six months in July after North Korea test-fired seven missiles into the sea between the countries.
In the wake of last week's purported nuclear tests, that ban has become indefinite and been extended to all ships of North Korean origin.
Lurching into the Niigata port in northern Japan once a month, the decrepit Mangyongbong-92 ferry was the only direct passenger service between the two countries and one of Pyongyang's few links with the outside world. It allowed agents to trawl the shops where the latest technology can be bought.
Many in Japan fear, however, that the measures to counter what was effectively an open secret may have come too late, after years of appeasing North Korea. Japan was nervous about provoking its volatile neighbor, and worried that it would be seen as harassing its 600,000-strong Korean minority.
Keiichiro Asao, a leading figure in the opposition Democratic Party of Japan, raised the issue as far back as 1998, supporting a failed bill that would have prohibited exports to North Korea.
"There was something of a taboo on the issue. We could have and should have done more to stop it at an earlier date," Mr. Asao said.
"Importing from Japan was very crucial to North Korea's weapons programs. Without Japanese technology, they wouldn't have been able to produce their nuclear weapon or their long-range missiles."