Twice, since August, India has found North Korean merchant ships illegally at anchor in Indian waters. In both cases, the captains said they had stopped to deal with a maintenance issue. Subsequent, rather thorough, searches of the North Korean ships discovered nothing. Nor did interrogation of the crews. So the two ships were allowed to go on their way, with a warning to alert the Indian coast guard the next time they were forced to drop anchor in Indian waters.
North Korea is under UN sanctions, and all nations have permission to search North Korean ships that come their way. Of course, all nations have always been able to search any foreign ships that enter their waters. But the UN sanctions provide more opportunities on the high seas (international waters.)
Meanwhile, South Korean, American, Egyptians and others have also come up empty after inspecting North Korean merchant ships. Many intelligence analysts believe that North Korea mainly sells the services of its people (for military or scientific projects) or items that can be shipped by air. North Korea is also known to have good smuggling skills, and has often shipped goods by rail or truck into China, then moved them by a non-Korean ship to its destination. It's hard to know where to search under these conditions.