The Unknown Rebel Tank Man — This famous photo, taken on 5 June 1989 by photographer Jeff Widener, depicts an unknown man halting the PLA's advancing tanks near Tiananmen Square.

On June 4, 2009, China will mark the twentieth anniversary of the Tiananmen Square Massacre — referred to in Chinese as the June Fourth Incident — in Beijing, People's Republic of China (PRC), that took place from April to June 1989.

The protests began in mid-April after the death of Hu Yaobang, a pro-market, pro-democracy and anti-corruption official who died on April 15, 1989. On the evening of Hu's funeral, as many as 100,000 mourners filled Tiananmen square.

During the seven weeks of protests, China's militant response to the protesters left many civilians dead and injured.

The official number of people who died as the result of the pro-democracy protests stands at 241, but unofficial numbers suggest that as many as 2,600 people died and as many as 7,000 people were wounded.

UPDATE: On Tuesday, June 2, 2009 reports emerged that China had blocked access to multiple social networking sites — including Twitter, Hotmail, Flickr, Bing, YouTube, Blogspot, Tumblr, Livejournal, Xanga, Wordpress, Friendfeed, and Windows Live ahead of the Tiananmen anniversary.

In preparation for the 20th anniversary of the Tiananmen Square Massacre on June 4th, China has started to block a number of web sites, including Twitter, Flickr, Blogger, Hotmail, and Microsoft's new search engine Bing. Tech-savvy Internet users in China, of course, know how to circumvent the Great Firewall, but for the large majority of Chinese Internet users, these sites will remain blocked for the foreseeable future. In addition to these high-profile sites, the Guardian also reports that the Great Firewall now also blocks access to more than 6,000 online forums affiliated with colleges and universities.