China Blocks Twitter, Hotmail and Flickr

China has ramped up Internet censorship as the anniversary of the Tiananmen Square massacre approaches — China's 300 million netizens can no longer access Twitter, Hotmail or photo-sharing site Flickr, among others.

This 20th anniversary marks the climax of student protests that ended in Beijing on June 4, 1989, when Chinese tanks and troops finally moved to crush protesters after seven weeks of peaceful demonstrations. Estimates of deaths range up to the thousands, and the event remains a highly sensitive political issue for China today.

China has long maintained its "Great Firewall of China" to block online sites or material that it deems objectionable or a threat to social stability. But unlike the historical Great Wall that was built to keep out nomadic invaders, the new Great Wall is intended to help China fight the unwanted effects of an increasingly interconnected world, not to mention web-savvy citizens.

That does not mean China has rejected the Internet by any means — the Chinese government embraces all the commercial and communication-enabling aspects, so long as they don't upset the current order. It has even apparently made use of hackers to probe the secrets of other nations such as the United States.

Still, Chinese netizens have already sparked some social unrest, including a series of taxi driver strikes that spread across the country at the end of last year.