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How China filters the Internet

China, world's biggest prison for cyber-dissidents, has developed very sophisticated technology for intercepting and censoring Internet content. Any topic that is not consistent with Communist Party ideology is censored in China.

Internet users in China trying to access information related to Taiwanese and Tibetan independence, the Dalai Lama, Falun Gong spiritual movement, Tiananmen Square, SARS, opposition political parties, and anti-Communist movements will find themselves out of luck.

CNN, using data from Reporters Without Borders, The OpenNet Initiative and China Internet Network Information Center, reports on how Chinese authorities intercept and censor content transmitted through Web pages, blogs, forums, bulletin boards and e-mail. Read interesting excerpts from the CNN report.

Every Chinese person using Internet must register with the local police department within 30 days.

Cybercafés (net bars) in China are required to keep detailed logs of customers' online activity on file for 60 days. If a user tries to access forbidden Web sites, a café must disconnect the user and file a report with state agencies.

People cannot use cyber services without an identification card, which is kept on record for at least 60 days. Children under 16 are not allowed in cybercafés.

ISPs must track who's online and what pages are visited. Customers' account numbers, phone numbers and IP addresses must be kept on file.

E-mail is filtered by service providers. Body text and subject lines are scanned and blocked if anything objectionable is found.

Chinese search engines monitor content by keyword and remove offending Web sites. Blog service providers do not let posts with certain words be published, and blogs are also censored manually.

Internet content is filtered by domain names and URLs which are blocked if they contain words or combinations of letters similar to those on the list of blocked topics.

Because a Web site can be reached by a URL or an IP address, China blocks both with technology and tricks such as TCP connection termination and "ZeroWindow" condition.

In addition to the above measures, volunteers, guided by ISP employees, monitor Web sites, chat rooms and bulletin boards to prevent prohibited language from being published.

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Read: CNN Technology - Learn how China intercepts and censors online content