China has blocked WhatsApp, security experts confirmed today to The New York Times. Over the past few months, WhatsApp has experienced brief disruptions to service, with users unable to send video chats or photos. Now, even text messages are completely blocked, according to Nadim Kobeissi, an applied cryptographer at Symbolic Software, a Paris-based research firm that also monitors digital censorship in China.

“Essentially, it seems that what we initially monitored as censorship of WhatsApp’s photo, video and voice note sharing capabilities in July has now evolved to what appears to be consistent text messaging blocking and throttling across China,” Kobeissi told The Verge.

Kobeissi found that China may have recently upgraded its firewall to detect and block the NoiseSocket protocol that WhatsApp uses to send texts, in addition to already blocking the HTTPS/TLS that WhatsApp uses to send photos and videos. He said, “I think it took time for the Chinese firewall to adapt to this new protocol so that it could also target text messages.” His company noticed the app disruptions beginning last Wednesday.

The move is a blow to Facebook, which has been banned in China since 2009 and owns WhatsApp. With the blocking of WhatsApp, Facebook’s only remaining stake in China is the Colorful Balloons app that it stealthily released last month.

The heightened censorship coincides with the upcoming 19th National Congress of the Chinese Communist Party. WhatsApp may have been a target because the app offers end-to-end encryption, which keeps users’ messages private. In contrast, other domestic Chinese apps like WeChat provide all users’ personal data to the Chinese government. WeChat, which already has 963 million active users, stands to benefit from one of its last foreign competitors being pushed out of the market. WhatsApp refused to comment.