• An international cyberattack crippled tens of thousands of computer systems in a hacking reminiscent of last month’s WannaCry attacks.

The outbreak started in Ukraine, where several ministries, banks and metro systems were crippled, along with radiation monitoring at the Chernobyl nuclear plant. It spread to other countries, including Russia, the U.S., France and Spain.

The hackers appeared to have used the same leaked N.S.A. tools that were deployed in the WannaCry attacks. Security experts are demanding that the American intelligence agency help the rest of the world defend itself against the weapons it created.