Microsoft has approached the issue with “tremendous sensitivity and a canny awareness of what the issues would be,” said an industry official familiar with Microsoft’s plans, who like several people interviewed for this story spoke on the condition of anonymity because they weren’t authorized to discuss the issue publicly. The company has “a long track record of working successfully with law enforcement here and internationally,” he added.

The changes, which give the authorities access to addresses and credit card numbers, have drawn quiet applause in law enforcement circles but hostility from many activists and analysts.

Authorities had for years complained that Skype’s encryption and other features made tracking drug lords, pedophiles and terrorists more difficult. Jihadis recommended the service on online forums. Police listening to traditional wiretaps occasionally would hear wary suspects say to one another, “Hey, let’s talk on Skype.”