LOS ANGELES — It was three days before Thanksgiving, the beginning of a quiet week for Sony Pictures. But Michael Lynton, the studio’s chief executive, was nonetheless driving his Volkswagen GTI toward Sony’s lot at 6 a.m. Final planning for corporate meetings in Tokyo was on his agenda — at least until his cellphone rang.

The studio’s chief financial officer, David C. Hendler, was calling to tell his boss that Sony’s computer system had been compromised in a hacking of unknown proportions. To prevent further damage, technicians were debating whether to take Sony Pictures entirely offline.

Shortly after Mr. Lynton reached his office in the stately Thalberg building at Sony headquarters in Culver City, Calif., it became clear that the situation was much more dire. Some of the studio’s 7,000 employees, arriving at work, turned on their computers to find macabre images of Mr. Lynton’s severed head. Sony shut down all computer systems shortly thereafter, including those in overseas offices, leaving the company in the digital dark ages: no voice mail, no corporate email, no production systems.

A handful of old BlackBerrys, located in a storage room in the Thalberg basement, were given to executives. Staff members began to trade text messages using hastily arranged phone trees. Sony’s already lean technical staff began working around the clock, with some people sleeping in company offices that became littered with stale pizza. Administrators hauled out old machines that allowed them to cut physical payroll checks in lieu of electronic direct deposit.