BEIJING -- Some websites, including ones with pornography, that were previously blocked by China's Internet censors were accessible inside the country Friday, though reasons for the change were unclear.
But China on Friday blocked Web service Foursquare, which lets users alert friends to where they are through their cell phones. The reason was not known, but many users had been "checking in" from Tiananmen Square to mark the anniversary of a bloody 1989 government crackdown on student-led pro-democracy protests.
Discussion of the event still is taboo in China and the Communist government is highly sensitive to any commemoration activities.
Beijing encourages Internet use for business and education but tries to block material deemed subversive or pornographic and operates an extensive system of Web monitoring and censorship. The government has launched repeated crackdowns against online pornography, calling it unhealthy and harmful.
But many Chinese and foreign-language pornography sites were accessible Friday and reports said they were apparently unblocked earlier this week. Other newly unblocked sites included Voice of America, video-sharing site Vimeo and URL shortening site bit.ly.
While video sharing site YouTube remained inaccessible as is routine in China, a pornographic knockoff -- YouPorn -- became available.
China's message boards, where many of the country's 400 million-plus Internet users trade information and gossip, were notably quiet about the newly unblocked sites. However, at least one posting on the topic could not be opened, indicating it was deleted by site administrators or government censors.
Wen Yunchao, a popular blogger who writes about social issues and the Internet, said most experienced users who want to watch pornography have always been able to access it using widely available proxy servers designed to scale the "Great Firewall."
"People who want to see porn, they'll always find a way to get to it," he said.
For example, "Xingqu," which Wen described as a major Chinese pornography site, had been blocked for more than five years but visitor numbers have not increased dramatically since it became available in recent days, he said.
It was not known whether there was a change in policy or if the newly available sites were related to a technical problem. Calls to multiple offices at the Ministry of Industry and Information Technology rang unanswered Friday.
"I think it's totally just a glitch. These things have happened often before. (Censors) screw up and some site will suddenly become available for a day or two days and then be back to normal again. There's never any rhyme or reason to it," said Kaiser Kuo, a Beijing-based technology analyst. "It's almost certainly not deliberate policy."
The sites became available amid a "sweep out pornography and prostitution" campaign in Beijing which has resulted in the closure of several nightclubs and karaoke parlors.
Chinese society has become increasingly open toward sex in recent years, but it is still rarely discussed openly. Underscoring enduring traditional attitudes, a college professor accused of organizing a swingers' club was sentenced last month to 3 1/2 years in prison on charges of group licentiousness.
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