Chinese authorities have apparently squelched another service — Facebook‘s WhatsApp text-messaging service.

The popular app — more than a billion people use WhatsApp, at least until the China ban — opens up an encrypted communication channel between two people. That encryption protects your privacy but also makes life hard for law enforcement, spies, and other forms of government snooping.

China started blocking the service Wednesday but fully blocked it Monday, according to researcher Nadim Kobeissi‏ of Symbolic Software, which monitors such services’ availability. It appears China is blocking the encrypted communications specifically, he told The New York Times.

Plenty of other services have been blocked in China, including Google search and Facebook’s social network.

WhatsApp declined to comment. Kobeissi and the Chinese government didn’t immediately respond to a request for comment.

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