BEIJING – At first, Liu Xiaoyuan just fumed when his online journal postings disappeared with no explanation.
Then he decided to do something few if any of China's censored bloggers had tried. He sued his service provider.
"Each time I would see one of my entries blocked, I'd feel so furious and indignant," said Liu, a 43-year-old Beijing lawyer. "It was just so disrespectful."
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Liu's frustration is hardly unique. For China's 162 million Web users, surfing the Internet can be like running an obstacle course with blocked Web sites, partial search results, and posts disappearing at every turn.
Blog entries like Liu's, which mused on sensitive topics such as the death penalty, corruption and legal reform, are often automatically rejected if they trigger a keyword filter. Sometimes, they're deleted by human censors employed by Internet companies.
In the lead-up to the sensitive Communist Party Congress, which convenes Monday to approve top leaders who will serve under President Hu Jintao through 2012, authorities have been casting an even wider net than usual in their search for Web content they deem to be politically threatening or potentially destabilizing.
"What you see now is unprecedented," said Xiao Qiang, director of the China Internet Project at the University of California, Berkeley. "They are forcing most of the interactive sites to simply close down and have unplugged Internet data centers. These are things they haven't done before."
Thousands of sites suddenly went offline in August and September when Internet data centers, which host Web servers, were shut down.
In three cities, some services were temporarily cut off, while some interactive Web sites remain unplugged — until after the congress.
It's not uncommon for authorities to crack down on public opinion before party congresses, which are held every five years.
In an increasingly wired China, political rumors and speculation that used to end up in Hong Kong's more liberal media are now often found circulating first in Chinese cyberspace.
At the party congress, there's plenty of opportunity for commentary, speculation and gossip.
"Who's going to be up and who's going to be down? Who's going to retire and who's going to be in the Politburo? The losers in the Internet age aren't necessarily going to go down quietly," said Xiao.
The government has built a patchwork system of controls that include software to root out offensive keywords and block blacklisted Web sites.
Government censors, known as Net nannies, surf the Web looking for pornography, subversive political content or other illegal material.
Major Internet portals like Sohu.com Inc. and Sina Corp. employ their own censors to make sure nothing runs afoul of government restrictions.
China is among a handful of countries that have extensive filters for political sites.
Iran, Myanmar, Syria, Tunisia and Vietnam also strictly block political content, according to the OpenNet Initiative, a collaboration between researchers at Cambridge, the University of Oxford, Harvard University and the University of Toronto.
In a report this week, Reporters Without Borders said China's Internet censorship system "is unparalleled anywhere in the world and is an insult to the spirit of online freedom."
Commercial sites that don't comply with censorship orders are criticized, fined, forced to fire the employee responsible for the error, or closed down, the Paris-based group said.
A point system is also used to keep track of compliance, with sites that rack up a certain number of demerits at risk of losing their business licenses, it said.
To underscore its determination, the government also imprisons people who mail, post online, or access politically sensitive content within China.
Reporters Without Borders says 50 Chinese "cyber dissidents" are currently in prison.
All the controls reinforce a climate of fear and obedience that keep most Internet users in line, experts said.
But if self-censorship fails, "Sohu will protect you from yourself," said Rebecca MacKinnon, a new media expert at Hong Kong University.
Liu, the Beijing lawyer, did not want to be protected. He has tried to sue Sohu for breach of contract for blocking nine of his blog entries.
Yang Bei, a Sohu spokeswoman in Beijing, said the company had no comment on the case.
Liu insists the postings conformed with Sohu's user guidelines as well as Chinese law.
He said that identical material posted to his Sina blog was not blocked. He is not asking for compensation, only to have his entries restored.
A Beijing district court dismissed his suit in August, saying that it did not meet unspecified criteria. His appeal is pending with the Beijing No. 1 Intermediate Court.
Despite the controls, Chinese cyberspace is also a surprisingly dynamic environment with online auctions, film and music downloads, social networks, huge virtual gaming populations and even spirited debate on social and political issues — though often conducted in protective double speak.
"You don't say 'tanks in Tiananmen,'" explains Xiao, referring to the 1989 military crackdown on democracy protesters. "You say 'the tractors that came into the city.' You don't say 'press freedom,' you say 'press professionalism.'"
Anxiety over such veiled conversations likely prompted the closure of several data centers last month, a move that affected thousands of small personal and commercial sites and warned millions of others.
The centers were told the shutdown was part of a larger campaign to clean up the Web ahead of the congress.
MacKinnon said the government appears afraid that something from one of those smaller sites will "jump out and bite the regime."
An employee with the Zitian Internet Data Center in the central city of Luoyang who would only give his surname, Feng, said its servers were unplugged on Aug. 23 and resumed on Sept. 5.
But interactive sites, such as bulletin boards and blogs, were closed until after the congress, which is expected to last about 10 days, on orders from state-run China Telecom, he said.
Shanghai's Waigaoqiao Internet Data Center was shut down Sept. 3-14 on orders from a China Telecom subsidiary, said an employee named Tang. Again, customers were told their interactive sites could reopen after the congress.
Another in the southeastern city of Shantou was also shuttered around the same time.
A Chinese blogger writing in English under the name Moonlight, catalogued the shutdowns in a post titled "Chinese Internet censorship goes crazy."
Xiao from Berkeley said the measures were intentionally heavy-handed.
"It's overkill to scare other people. Now the other IDCs are shaking," he said.
China's Ministry of Information Industry, which is the main government body in charge of the Internet, and China Telecom did not respond to a request for comment about the Internet data center shut downs.
Meanwhile, Chinese bloggers who have been censored say they've been "harmonized," a nod to President Hu's goal of creating a "harmonious society."
One sarcastic Chinese blogger called Xiucai — or the Scholar — mockingly posted a banner to his or her site on Sept. 4 saying: "Joyfully welcome the 17th Party Congress, building a harmonious society together. The Scholar is a good comrade. This site has temporarily shut down comments and forum features."
Within two weeks, Xiucai took the banner down too.