The attacks, which include efforts to hack into banks, utilities and oil and gas companies, began in 2017, according to researchers at the cybersecurity company McAfee, a time when tensions between North Korea and the United States were flaring. But even though both sides have toned down their fiery threats and begun nuclear disarmament talks, the attacks persist…

The exact motive of the attacks was not clear. They were well-researched and highly focused and, in many cases, aimed at engineers and executives who had broad access to their companies’ computer networks and intellectual property.

The vast majority were in the United States, with the most frequent marks in Houston, an oil and gas hub, and New York, a finance hub. Other major targets included London, Madrid, Tokyo, Tel Aviv, Rome, Bangkok, Taipei, Seoul and Hong Kong. Russia and mainland China, two countries that have maintained cordial relations with North Korea, were relatively untouched.