The US government has expressed concerns about the so-called Great Cannon censorship tool reported to be in use in China, and has told the country that it wants answers about the weapon.
The Cannon has been used a couple of times, most notoriously in a long-running assault on code-sharing site GitHub.
It is used by the Chinese government to limit local access to overseas information, particularly US information. The GitHub incident showed that the tool is effective.
After 113 hours of sustained DDoS attacks our defenses are holding. We will keep our status at yellow until the threat has subsided.— GitHub Status (@githubstatus) March 30, 2015
The problem of the Great Cannon was raised during a press session at the White House. State Department spokesman Jeff Rathke suggested that its use runs counter to a free, secure and open internet.
"The US is committed to protecting the internet as an open platform on which all people can innovate, learn, organise and communicate, free from censorship or interference," he said.
"And we believe that a global, interoperable, secure and reliable internet is essential to realising this objective.
"And we view attacks by malicious cyber actors who target critical infrastructure or US companies and US consumers as threats to national security and to the economy of the US."
Rathke said that the US is looking into the censorship tool as part of its regular criticism of China's internet stance, and has asked the country for answers.
"The cyber attack manipulated international web traffic intended for one of China's biggest web services companies and turned it into malicious traffic directed at US sites," he said.
"We have asked the Chinese authorities to investigate this activity and provide us with the results of their investigation.
"At the same time, we're working with all willing partners to enhance cyber security, promote norms of acceptable state behaviour in cyber space, and to protect the principle of freedom of expression online."
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