Thursday marks the 20th anniversary of the Tiananmen Square uprising in which the Chinese military brutally crushed protestors, possibly killing thousands of students, activists, and citizens. The Chinese government, however, has quashed public attempts to mark the occasion with extreme security moves. Officials have instituted passport checkpoints to bar foreign journalists, photographers, and TV camera operators from entering the square, banned social networking and image-sharing websites like Twitter and Flickr, blacked out foreign news channels such as CNN during broadcast segments on Tiananmen, and put dissidents under house arrest or forced them to leave Beijing. Wu'er Kaixi, the No. 2 wanted student leader from that day, who has since been in exile, tried to enter China to turn himself in to authorities so that he could see his parents, who are not permitted to leave China, but he was denied entry.