BEIJING -- Word leaked out slowly, spread by Web-savvy folks on Twitter: Internet porn that once was blocked by Chinese government censors was now openly available.
"Are they no longer cracking down on pornographic websites? A lot of porn sites and forums are accessible," technology blogger William Long wrote on his feed.
Messages like that startled Chinese Web surfers, long accustomed to the authorities' Internet blockades. The country had been in the midst of highly publicized anti-pornography sweeps, and there had been no announcement of any change in government policy.
Yet eight weeks later, the porn sites are still accessible. Still unanswered are questions about whether it's an official change in policy, a technical glitch or some sort of test by the usually disapproving Chinese Internet police.
"This has never been done with the [Chinese] Internet before," said Beijing-based Internet analyst Zhao Jing, who goes by the English name Michael Anti.
Whatever the reason, the change has thrown into sharper relief what many people see as the main mission of China's aggressive Internet censors: blocking sites and content that might challenge the political authority of the communist government. Websites about human rights and dissidents are also routinely banned.
"Maybe they are thinking that if Internet users have some porn to look at, then they won't pay so much attention to political matters," Anti said.
The government has not said why the sites were unblocked. Repeated calls to the Ministry of Industry and Information Technology went unanswered, and the Ministry of Public Security and State Council Information Office -- all involved in Web monitoring -- did not respond to faxed requests for comment.
China has the world's largest online population of 420 million -- more than the entire U.S. population. While the Internet is the most freewheeling of tightly cosseted media in China, the government has the most extensive Internet policing system, from technical filters that block sites based on certain words to human monitors who scan bulletin boards and micro-blogging posts.
Censorship issues led Google Inc. to clash publicly with China earlier this year and eventually close its China search engine and redirect users to Hong Kong.
Tired of the controls, many Chinese have learned to get around "the Great Firewall," or GFW, as the system is known.
Few Chinese will admit to surfing for porn because it is illegal. Many sites are still inaccessible, and of those, sites that somehow evade control are usually blocked within hours. But the demand is there.
"The more they restrict something, the more people pay attention," said a 29-year-old employee at a state-owned logistics company who did not want to be identified because he surfs for porn on business trips.
Sites that suddenly became available around late May include the English-language YouPorn and PornHub, along with numerous Chinese sites offering downloads, though Anti and others say well-known Chinese-language sites remain blocked.
Wen Yunchao, a popular blogger who writes about social issues and the Internet under the name Beifeng, said even more porn sites have become available in recent days, including a well-known Chinese site called "Xingba," or "Sex Bar."
"In the past, the GFW would use pornography as an excuse" for censorship, Wen said. "Now they're not even trying to cover it up."
Chinese society's conservative attitudes about sex are rapidly changing, especially among the young, who make up the majority of Internet users. The trial and conviction this year in southern China of a college professor who used the Internet to organize orgies touched off a debate about privacy and sexual freedom.
A poll of 900 female graduates at 17 Shanghai universities showed that 70 percent think one-night stands aren't immoral, and more than half said they could understand if a girl became a rich man's lover, according to state media.
Liao Shengqing, a journalism professor who led the study, was cited by the People's Daily newspaper as saying that "students' attitudes come from their respect for individual privacy. They regard sex as a private matter and respect other people's choices."
Some speculate the proliferation of social networking sites and Twitter-like services was taxing the Great Firewall, requiring the government to unblock some porn sites to free up capacity for other snooping.
"I think when the GFW realized they were not able to block all domain names, they reallocated resources to block more urgent or political sites," said Long, the tech blogger who is based in Shenzhen and would not give his real name in Chinese.
As part of the change, employees in the office that cracks down on pornography and unauthorized publications no longer have to report overseas-based porn sites to police because of the difficulties in tracking down Chinese involved, the state-run magazine Oriental Outlook reported in May. Censors only need to note the sites, the report said.
Because a dozen or so agencies regulate the Internet in China, the porn availability may have resulted from a shifting of responsibilities, said Xiao Qiang, director of the Berkeley China Internet Project at the University of California-Berkeley.
"The Great Firewall is not that serious toward blocking porn sites. It never was," he said. The true targets, he said, include political information, current affairs, negative reports about leaders, and anything that may trigger a protest.
"That kind of information is where the censorship focus is really," Xiao said. "Porn, they're just halfheartedly doing it."