For nearly three weeks, Baltimore has struggled with a cyberattack by digital extortionists that has frozen thousands of computers, shut down email and disrupted real estate sales, water bills, health alerts and many other services. *snip* Since 2017, when the N.S.A. lost control of the tool, EternalBlue, it has been picked up by state hackers in North Korea, Russia and, more recently, China, to cut a path of destruction around the world, leaving billions of dollars in damage.