Ransomware Attacks Grow, Crippling Cities and Businesses

SAN FRANCISCO — New Orleans’s city government crippled. A maritime cargo facility temporarily closed. Hospitals forced to turn away patients. Small businesses shuttered.

The cause in each of these incidents: ransomware attacks. In recent years, hackers have taken to locking down entire computer networks and demanding payments to let users back into their systems.

The frequency of ransomware attacks — among the scariest and most costly online assaults — has been hard to pinpoint because many victims quietly pay off their attackers without notifying the authorities.