What does it mean when an entire country is cut off from the rest of the Internet?
If you're in China, it can be one of two things: technical error, or a test of a government Internet "kill switch."
Internet users across China were unable to access foreign websites for about two hours yesterday, beginning at 10:40 a.m. local time (Wednesday evening in North America). At the same time, users in Hong Kong and Japan began to have trouble viewing Chinese websites.
Web surfers in China had no trouble accessing sites within the country, and they used websites and China's domestic Twitter-like services to inform each other about the outage and speculate as to its cause.
"All foreign websites are inaccessible!" tweeted Lee Kai-Fu, a Taiwanese-American former Microsoft and Google executive who is one of China's most prominent tech entrepreneurs, according to the Guardian.
"I can access Yahoo China, but not Yahoo HK, Yahoo Taiwan, or any other overseas version of it," wrote Shanghai-based Tech in Asia reporter Steven Millward.
There were rumors that the outage was related to Wednesday's massive earthquake in the eastern Indian Ocean, or at least some problem with an undersea telecommunications cable.
"Around 10:40 a serious problem occurred with China telecom's backbone network, leading to sites in Hong Kong, Japan, America, Korea, Australia, and Singapore being inaccessible. This was caused by a malfunction in China's backbone network. It is under repair..." tweeted a manager at Sohu, one of China's largest search engines, according to Tech in Asia.
But others weren't convinced.
"Some, but not all, VPNs still working ... so it is not a cable issue. Somebody slammed the door," tweeted a Westerner named David Wolf, as quoted by Tech in Asia.
Wolf was referring to the virtual private networks (VPNs) Web users in China use to get around the "Great Firewall" that periodically blocks access to Western sites and services, such as Facebook, Twitter, Google, Flickr, YouTube, Wikileaks and many pornographic sites.
A day later, others were beginning to agree. Officials at two China's two largest telecommunication companies, China Telecom and China Unicom, told Tech in Asia that there was nothing technically wrong with their networks.
An executive with the American Web-performance and security company CloudFlare told the Wall Street Journal that while China Telecom and China Unicom's global Web traffic plummeted for two hours yesterday, smaller Chinese telecommunication companies were unaffected.
CloudFlare's engineers also noticed that only standard Web-protocol HTTP traffic was being choked.
Internet traffic that uses other protocols and ports, such as Skype voice communications, back-channel communication between networking devices and regular email, was flowing unimpeded through China Telecom and China Unicom even while Web exchanges were being stopped at the border.
"No one is quite sure what happened," an unnamed official at a Chinese internet company told London's Daily Telegraph. "It seems that everyone's best guess is that they were upgrading the Great Firewall and something glitched during the process. My own theory is that they were testing the great switch to turn off the Internet."