Twenty years ago he was the ultimate symbol of a peaceful democratic protest that went terribly, fatally wrong: a lone Chinese man in a simple white button-down shirt, carrying two plastic shopping bags, staring down a column of tanks.

Tank Man — his identity has never been determined — shot to worldwide fame that day for stopping those tanks, hours after they had brutally crushed student-led protests on Beijing's Tiananmen Square. Hundreds — possibly thousands — died in the early-hours protest on June 4, 1989, an event that still remains a forbidden topic in Communist-governed China.

Pictures of Tank Man's courageous efforts and other information about the crackdown are still officially censored in China. But now, 20 years on, modern technology and the wide reach of social networking sites like Facebook are providing curious students with the information they were previously denied.

"In this, 20 years ago, China strove for democracy and freedom. The government killed our compatriots, university students and citizens," wrote a woman identifying herself as Bonnie Wong on the Facebook fan site Tank Man, one of several forums that have popped up ahead of the 20th anniversary of the crackdown.

"For 20 years, more than a few have entered the political arena who are the real villains, hypocrites who put on a false show of great peace and bury their consciences in a fiery pit. They control the government, they control media, they hold on to education, they control writing," wrote another Facebook member who calls himself Jonathan Siew.

The vast majority of Chinese youth show no outward knowledge of what happened 20 years ago, a fact that pains the still-mourning relatives of those who were killed.

"This is a cruel reality — young people do not know the truth," said Ding Zilin, a retired professor whose 17-year-old son was shot dead that night. "The government hides the truth from children and keeps it as a sort of forbidden zone. It isn't taught in classrooms."

But in the anonymity of the online world, Internet-savvy youths use mirror sites and proxy servers to explore alternative versions of the official history and to discuss their own frustrations with their government's clumsy efforts at censorship.

China's censorship of Web sites deemed harmful to its government and security is known as The Great Firewall; this week it blocked access to Twitter, Bing.com, the photo-sharing Web site Flickr and, briefly, Hotmail. Other sites, including YouTube and blog providers like Blogspot and Wordpress, are routinely barred.

But frequent Twittering and Facebooking from Chinese users on the eve of the June 4 anniversary proved there are many ways around the censors' efforts.

One Twitterer, identified as freemoren, posted regular updates of what was happening exactly 20 years ago on the square; others shared links to Western documentaries and newspaper articles about the Tiananmen massacre; some even speculated about how many packages Tank Man held in his hands as he faced down the tanks.

As in the West, there are few to no clues about Tank Man's identity and fate. Chinese users are reluctant even to express their opinions on his actions, or to reveal their real identities, in case they are tracked down and questioned by police.

"Everyone, be very safety conscious!" a Chinese Twitterer identifying himself as flypig warned. Code words abound; the government censors are known as "river crabs," and the anniversary itself is referred to as "TAM" or "ATM" or "8964."

While information is available to those who seek it out, the next generation is still a long way from being able to express opposition to the Tiananmen massacre publicly. The square was under heavy security this week, and news crews were chased away. At least one prominent university's student association was reported to be advising students to stay home and resist any temptation to protest.

"Most people are certainly affected by the public opinion control. The effect is obvious," tweeted a Chinese user identifying himself as Hosven. "Few in our generation of people know about 8964. Those who understand its seriousness are less."

Click here to see a Facebook page dedicated to Tank Man.