The tightening of China’s control over Internet traffic across its borders continues, with loopholes closing and apparently punitive disruption of connections used to “jump the wall”.

Flipboard is a “personalized, social magazine” app for iPad which, by aggregating content from Twitter and Facebook, has given users in China indirect access to these blocked services. Techcrunch, however, reports that this loophole has now been closed:

As of today certain aspects of the Flipboard experience have been blocked for Chinese users, at the very least access to Facebook and Twitter according to Flipboard CEO Mike McCue. While direct access to Facebook and Twitter is routinely blocked in China, the Flipboard app talked to its own US-based servers, which in turn talked to Twitter and Facebook so this block is particularly interesting.

“Lots of folks in China had been using us happily until now,” McCue said, “Guess we had unwittingly poked a hole in their wall which has now been shut down… Presumably unless we block Facebook and Twitter ourselves in China.” The iPad app is still available in the Chinese app store ….

“I can now confirm Flipboard itself is being blocked. All services (not just Facebook and Twitter) no longer work. [Users] used to be able to login to Facebook and Twitter using VPN. Now with our servers blocked, even if you had successfully logged in, we can’t show data. Also, users who had setup Flipboard from outside china used to be able to use Facebook and Twitter when within china. That is no longer the case.”

Global Voices Advocacy, meanwhile, describes new measures to discourage use of corporate and academic computers to access blocked sites overseas:

A number of Chinese netizens report that since May 6 2011 visiting overseas website via China Telecom and China Unicom has become highly unstable. This time the disruption mainly affected corporate connections, including university, while ADSL connection at home performs normally.

Some technology bloggers point out that the Great Fire Wall is now able to monitor data flow of local IP and impose restriction when it detect large amount of access to certain overseas IP addresses. Some are worried that the mechanism may result in a de facto white listing of overseas websites.

Prominent Technology blogger William Long points out that the blocking this time is targeted at corporate user in order to stop people from visiting overseas website via corporate network and connection.

A notice from the Chinese Academy of Sciences has confirmed netizens’ speculation:

CAS IHEP: Our faculty’s access to overseas websites have been disrupted in the past few days. Upon investigation, the reason is because some users have used circumvention tools to get access to illegal content, hence the public security bureau has black-listed our faculty’s IP. Here I remind everyone to follow the rule when using Internet, don’t use illegal means to get access to illegal information!

See also: “Shenanigans” as China Restricts VPN and Other Connections on CDT.