Today China is marking the anniversary of a particularly dark stain on its history with what has has become something of a new tradition: censoring all conversation about it from the internet.

Twenty-three years ago on June 4, 1989 China shocked the world by shooting into a crowd and killing hundreds of civilians during a peaceful pro-democracy protest in Tiananmen Square in Beijing. Amid the massacre cameras captured an individual act of heroism that became one of the most iconic images of the decade: the anonymous Tank Man, who stopped a convoy by standing in front of tanks and daring them to run him down.

The video played on repeat on daily news worldwide and the Tank Man became a national folklore hero, but today China is still trying to restrict conversation of the incident, lest anyone get any ideas.

Mashable reports that China’s state-employed web censors, of whom there are thousands, have spent the day scrubbing web searches and posts on Sina Weibo, China’s version of Twitter.

“Banned terms include ‘six four,’ ’23,’ ‘candle’ and ‘never forget,’” writes Mashable, and authorities are also blocking the emoticon of a candle, which represents mourning and solidarity.

China’s internet censorship is nothing new. Censors banned the word “Egypt” from searches during the Arab Spring, and Sina Weibo is actually based on system of points that rewards users for posting material deemed government-friendly and penalizes them for inappropriate content. These include messages about “formation of organizations, protests, demonstrations, mass gatherings and assemblies,” or even ones that “undermine ethnic unity.” Check out the whole list of offending topics here.

Below, watch the Tank Man face down an entire military convoy via YouTube—another service banned in China. It’s probably the most potent David and Goliath imagery every captured in modern news. The Tank Man disappeared immediately after the incident—whether he was jailed, executed or managed to escape is still unknown. But he remains one of the most badass protesters of all time.