BEIJING — It came as little surprise when, after the death of the dissident Liu Xiaobo last week, China’s vast army of censors kicked into overdrive as they scrubbed away the outpouring of grief on social media that followed.

The accounts of censorship have been mostly anecdotal. But systematic research from the Citizen Lab at the University of Toronto’s Munk School of Global Affairs shows that there was a “significant shift” in censorship techniques in the days after Mr. Liu’s death, particularly on WeChat, the popular messaging app from Tencent.

On WeChat, which has more than 768 million daily active users, the number of keyword combinations that were blocked greatly increased, according to the report that the Citizen Lab published on Sunday. Additions to the blacklist included general references to his death like “Xiaobo + died” in Chinese and in English, and even just his name “Liu Xiaobo,” effectively censoring any messages that mentioned him.

The Citizen Lab said it was also the first time that images were automatically filtered in private one-on-one chats on WeChat. Blocked images included photographs of Liu Xiaobo and of people commemorating him.