"Lots of unexpected things are going to happen," he says.
Forbidden words, stories
The most basic tool at the Chinese government's disposal — and, perhaps, the one most easily circumvented by dissidents — is to ban access within China to websites such as Voice of America or to certain stories that contain sensitive words and phrases. For example, several recent USA TODAY stories about Tibet are currently blocked within China.
Other censorship methods are more blunt. This month, Hu Jia, an activist on AIDS and other issues, was sentenced to 3½ years in jail for articles he wrote for Boxun.com, a U.S.-based Chinese-language website that is banned in China. At least 48 cyberdissidents are behind bars in China, according to Reporters Without Borders.
Chinese officials with the Ministry of Information Industry, the State Council Information Office and other agencies declined to comment on why China restricts content on the Internet.
Past explanations by the government focus on the need to prevent "harmful" content such as pornography and terrorism from reaching citizens.
Even those "hacktivists" who live outside the country apparently face risks. Peter Li — a Chinese-born, Princeton-educated computer specialist — says he learned that two years ago when he answered the doorbell at his home in suburban Atlanta.
Three men burst inside, beat him, bound him and gagged him with duct tape, he says. Speaking Korean and Chinese, they ransacked his filing cabinets and hauled off his two computers. They ignored a TV, a camcorder and other valuables.
The FBI and the local Fulton County, Ga., police still have not found the men responsible for the attack. But Li, who like Xia is a practicing member of Falun Gong, says it was an attempt by the Chinese government to shut him up.
"I know it wasn't a simple robbery," he says.
The Chinese government has denied any involvement in the raid on Li's home.
There are a range of other methods China has used to suppress information. Among them:
•Creating bottlenecks. In The Atlantic magazine last month, journalist James Fallows noted that Internet traffic to China is channeled through three computer centers — near Beijing, Shanghai and the southern city of Guangzhou.
In the USA, by contrast, the Internet is designed to avoid traffic jams by allowing information to flow from as many sources as possible. By building in chokepoints, Fallows wrote, "Chinese authorities can easily do something that would be harder in most developed countries: physically monitor all traffic into or out of the country."
•Checking Internet traffic for subversive material. This is done in much the same way police dogs sniff airport luggage for illegal drugs. The Chinese install "packet sniffers" and special routers to inspect data as they cruise past the chokepoints. If the detectors spot a Chinese Internet user trying to visit a suspect website — say, one run by Falun Gong — they can block the connection.
A frustrated user might get a message saying: "Site not found." Similarly, Web users can be stopped from leaving subversive comments in online forums. Sometimes they get notes back warning them to behave or apologizing for technical problems.