In the past few weeks, some of the biggest industries in the U.S. have been held up by cyberattacks. The first big infiltration was at Colonial Pipeline, a major conduit of gas, jet fuel and diesel to the East Coast. Then, J.B.S., one of the world’s largest beef suppliers, was hit. The so-called ransomware attacks have long been a worry. But who are the hackers and how can they be stopped? Guest: Nicole Perlroth, a reporter covering cybersecurity and digital espionage for The New York Times.