Hot on the heels of (reportedly) harnessing nuclear fusion and a slew of ballistic missile launches, South Korea’s intelligence agency is now reporting that Kim Jong-Un’s North Korea is developing an electromagnetic pulse (EMP) weapon. At a bare minimum, this EMP could theoretically damage electronic equipment south of the Korean DMZ. At higher power levels, a real EMP device can melt any electronic device or system within hundreds of miles. The EMP weapon would be part of North Korea’s larger cyberwarfare efforts, which have so far been mainly focused on gathering intelligence by hacking South Korean computer networks and devices.

According to South Korea’s National Intelligence Service (NIS), North Korea has purchased EMP weaponry from Russia, and is now developing its own in-house version. As you’d expect, given the sensitive nature of this information, we don’t have a whole lot of details about either the Russian EMP weapon or the DPRK’s homebrew variant. We can attempt to extrapolate some details from Russia’s previous EMP tests and what we know about EMP weapons in general, though.

As you probably know from The Matrix and various other action/sci-fi settings, electromagnetic pulses are the ultimate weapon against anything electronic — from telephone wires to the power grid to the computer chips that control cars, planes, and smartphones. Weaponized EMPs generally come in two forms: nuclear and non-nuclear. Non-nuclear EMPs are fairly weak (on the order of one million times weaker than their nuclear counterparts), but that’s not necessarily a bad thing if you’re just trying to knock out the electronics of a small, localized area (a military base or water pumping station, for example). At this point, we have no idea if North Korea has acquired nuclear or non-nuclear EMP tech from Russia — but as non-nuclear EMPs are pretty dull, let’s just assume the worst and assume that North Korea now has a nuclear EMP in its possession.

Standard nuclear bombs, like those dropped on Hiroshima and Nagasaki, create a huge amount of gamma radiation when they explosively fission atoms. This gamma radiation ionizes — strips electrons away from — atoms in the atmosphere, creating a huge mass of free electrons. These electrons are then deflected by the Earth’s magnetic field, creating a huge electromagnetic pulse — or E1, in EMP terms. The E1 induces very high voltages in just about everything, causing wires to melt, fuses to blow, and insulators to break down and become conductors. The E1 pulse is incredibly fast — just a few nanoseconds after the nuclear detonation.

There are also E2 and E3 pulses: E2 is fairly similar to lightning, and E3 is comparable to geomagnetic storms caused by solar flares (the nuke distorts Earth’s magnetic field, basically). Surge protectors generally protect against E2. E3 is hard to protect against, but its effects are generally only felt by larger electrical installations, such as power lines. The massively powerful E1 pulse — around 50,000 volts per meter, or a peak power density of 6.6 megawatts per square meter — is what knocks out the majority of your electronic infrastructure.

Because the E1 pulse is generated by gamma rays striking the atmosphere, the most effective nuclear EMPs are detonated at high altitude — around 250 miles (400 km) above Earth. This allows the gamma rays to spread out before they hit the atmosphere, creating a huge area of effect. The nuclear device doesn’t even need to be that big, either — in 1962, the USA tested a 1.44-megaton nuclear EMP (Starfish Prime) above the Pacific Ocean that caused electrical damage 900 miles away in Hawaii. Kiloton-yield nukes would still be very effective as well, and to maximize the size of the EMP it’s actually better for the nuke to be plain ol’ fission, rather than a thermonuclear fission-then-fusion device. If a big EMP was detonated above the USA, the E1 burst would probably melt most of the electronics within 1,000 miles or so. (Read: 500MW from half a gram of hydrogen: The hunt for fusion power heats up.)

The Soviet Union also performed some successful EMP tests in the early ’60s, fusing hundreds of miles of telephone wire and burning down a power plant (for some reason the Soviets performed the test over a populated land mass). Since then, though, as far as we know, there have been no further testing of nuclear EMPs by either the US or Russia. It’s fairly safe to assume that the world’s nuclear powers have developed advanced EMPs — the power to knock out a country’s infrastructure without frazzling millions of people is pretty awesome — but they’re impossible to test without giving away the game.

Which brings us back to North Korea. It’s unlikely that Russia would give Supreme Leader Kim Jong-Un a nuclear weapon. It’s possible that North Korea has its own fission device that it’s planning to combine with older Russian/Soviet EMP tech, and then detonate it over South Korea with one of its intermediate-range BM25 Musadan ballistic missiles. But really, how North Korea obtained an EMP isn’t all that significant. It’s now been more than 50 years since the first nuclear EMP detonations. With modern tooling and technologies, creating an EMP weapon isn’t particularly hard. For me, the fact that North Korea has tested or acquired a certain weapon of mass destruction is hardly surprising — for me, it’s much more surprising that the Supreme Leader hasn’t used any of them yet.

Now read: EMPs are scary, because we’re slaves of electricity