In early June North Korea test fired what it described as a new cruise missile called the Kumsong-3. It was obvious (from the pictures) that the missile was a Russian Kh-35 that had had been seen on one or two of the four of five large (over 1,000 ton) surface warships the North Korean Navy has that are capable of going to sea (but rarely do). The June test was from a mobile launcher (on tracks, carrying four missiles in canisters) and that was sort of new. The missile shown not only looked like a Russian Kh-35 but the data North Korea released showed it performing like a Kh-35, which Russia has been busy upgrading and marketing since the late 1990s.
By 2008 the Kh-35 (also known as the SS-N-25 or Switchblade) could be fired from helicopters, aircraft, ships, or land. Russia denies it sold the missiles to North Korea thus the only other likely source is one of the known foreign customers (Algeria, Azerbaijan, Burma, India, Iran, Venezuela, and Vietnam). Vietnam is building Kh-35 under license and Iran may be doing so without a license. Iran could have sent one or two Kh-35s to North Korea (the two countries have long exchanged missile tech) via air freight in the knowledge that North Korea had the resources to build its own unauthorized copies of Kh-35. The few Kumsong-3 Kh-35 clones seen in action could be using 1970s technology to do what they obviously did. These missiles use a simple jet engine and travel at up to 700 kilometers an hour. They can use inertial guidance or GPS and be programmed to change course. Terminal guidance can be as primitive as a 1960s era radar homing system. North Korean propaganda indicates the Kumsong-3 was far more high tech than it actually is. This sort of media stunt is something else Iran is good at and since the 1990s North Korea has been using this sort of thing a lot more. The media love it but historians note that it is an ancient scam. That is not news.
The Kh-35 is similar to the American Harpoon but lighter (610 kg/1,340 pounds, compared to 728 kg/1,600) and has less range (130 kilometers compared to 224 for the latest version of Harpoon). A 2015 Russian upgrade for the Kh-35 extended range to 260 kilometers and improved the guidance system (with two way communications for course changes and improved terminal homing).
The Harpoon entered service in 1977 and became one of the most widely used (and emulated) anti-ship missiles in the world, mainly because of reliability and constant upgrades. The Kh-35 was the Russian response and development did not begin until 1983. Work was stalled with the collapse of the Soviet Union in 1991. Russia announced the Kh-35 was available for export in 1996 but the Russian Navy did not start using it until 2003 and that was about when export sales and deliveries began to happen. In 2006 Russia announced it had put into service a land-based version of Kh-35 that could be operated from fixed or mobile (trucks or tracked vehicles) launchers. This is what North Korea did with its Kumsong-3 in 2017.
The June test was given considerable media exposure by the North Koreans. They knew that these tests are closely watched by the U.S., Japan and South Korea. North Korea wanted everyone to think that they had something similar to the latest (2015) version of the Kh-35. But it was also possible that all they had done was extend the range (a simple mod) and used an older terminal guidance system. North Korea had a small target ship out at sea, equipped with a radar enhancement device (which made the ship look larger, as if to imply an American destroyer or carrier). But the North Korean target was not moving and had no countermeasures. So it was a simple matter for a North Korean copy of the original (1990s) Russian Kh-35 design was used. In combat Western warships, which have lots of experience with missiles like this, have countermeasures and use them regularly in training.