Signal, the encrypted chat app, had stopped functioning in China as of Tuesday, in what appeared to be a block of one of the last major foreign messaging services still available in the country, where the internet is closely controlled.
Users in China on Tuesday morning reported widely that the app had stopped working. A New York Times test of the app in Shanghai and Beijing confirmed the reports. Signal did not respond to an emailed request for comment.
The outage appeared likely to be a government-led block. The app continued to work when users in the mainland logged on to the service via a virtual private network, software that routes their connections outside the country.
Signal allows messages to be sent with “end-to-end encryption,” which blocks anyone but the sender and receiver from reading the contents. The app has soared in popularity globally in recent months a fears have grown over data harvesting from large internet companies.
The likely block further limits communication options on China’s internet, where the government has built a sophisticated system of censorship and surveillance to control speech. Over the past 15 years, Beijing has steadily winnowed down the major foreign communication tools available to regular Chinese users. Services like Google’s Gmail, Facebook’s WhatsApp and Twitter are all blocked.
In recent years, Signal had grown a modest following in China among activists, journalists, lawyers and others as China’s top leader, Xi Jinping, has presided over a series of campaigns to crack down on the media, civil society groups and online speech broadly.
For years, it had been a parlor game among its users in China to guess why Signal, long a well-known tool for secret communications, remained unblocked. One theory was that it helped the authorities find who was trying to hide from government spies because, when first downloaded, the app sends the new user a text message that they could possibly track. Still, China’s government often waits for apps to reach larger scale before banning them. Last month, the social media site Clubhouse fell afoul of the blocks after it soared in popularity.