A couple of years ago, the journalist Nicholas Shaxson published a fascinating, chilling book titled “Treasure Islands,” which explained how international tax havens — which are also, as the author pointed out, “secrecy jurisdictions” where many rules don’t apply — undermine economies around the world. Not only do they bleed revenues from cash-strapped governments and enable corruption; they distort the flow of capital, helping to feed ever-bigger financial crises.

One question Mr. Shaxson didn’t get into much, however, is what happens when a secrecy jurisdiction itself goes bust. That’s the story of Cyprus right now. And whatever the outcome for Cyprus itself (hint: it’s not likely to be happy), the Cyprus mess shows just how unreformed the world banking system remains, almost five years after the global financial crisis began.

So, about Cyprus: You might wonder why anyone cares about a tiny nation with an economy not much bigger than that of metropolitan Scranton, Pa. Cyprus is, however, a member of the euro zone, so events there could trigger contagion (for example, bank runs) in larger nations. And there’s something else: While the Cypriot economy may be tiny, it’s a surprisingly large financial player, with a banking sector four or five times as big as you might expect given the size of its economy.

Why are Cypriot banks so big? Because the country is a tax haven where corporations and wealthy foreigners stash their money. Officially, 37 percent of the deposits in Cypriot banks come from nonresidents; the true number, once you take into account wealthy expatriates and people who are only nominally resident in Cyprus, is surely much higher. Basically, Cyprus is a place where people, especially but not only Russians, hide their wealth from both the taxmen and the regulators. Whatever gloss you put on it, it’s basically about money-laundering.