The mainland's "Great Cannon" programme can hijack incoming internet traffic and direct it against any website deemed unfriendly to the Communist Party.

China's 'Great Cannon' programme has been in development for about a year, sources say

The Beijing-backed programme hijacks incoming internet traffic and redirects it to 'unfriendly' websites, but move could harm big tech firms

The mainland's "Great Cannon" programme that can hijack incoming internet traffic and direct it against any website deemed unfriendly to the Communist Party, has been in development for about a year, three sources have said.

The tool marked a shift by Beijing towards an offensive strategy in censoring the internet, and could hinder attempts by mainland tech companies to take their brands to an international market, an expert said.

According to a report by the Citizen Lab at the University of Toronto released on Friday, the "Great Cannon" was aimed at shutting down websites and services that help mainland internet surfers bypass the "Great Firewall", which blocks domestic access to information the authorities deem sensitive.

It works by hijacking unwanted web traffic and redirecting it to websites of China's choosing in such large quantities that it can overwhelm servers and knock them offline.

"The system has been in operation for about one year, and it reflects a brand-new strategy since it's taking an offensive attitude rather than the Great Wall's tactics of focusing on defence," said the chief executive with a mobile technology firm, who has knowledge of the mainland's internet security efforts.

"It has proved to be efficient so far since the majority of its targets have been successfully disrupted."

Beijing has intensified censorship efforts in the past months, including cracking down on the use of virtual private network (VPN) connections, which allow mainlanders to bypass internet restrictions, and strengthening the "Great Firewall".

"The upgrading work was huge and lasted for a few months," said a national security source. "But it didn't work eventually. As we upgraded the firewall system, those hostile groups [overseas] also upgraded their service to help mainlanders bypass the blockages," the security source said.

In March, an advocacy group that monitors web censorship on the mainland, said it was suffering a distributed denial-of-service attack. The researchers said the attack was launched through a program that hijacked internet traffic to the big Chinese search engine Baidu and used it to flood the website in an effort to knock it offline.

The Citizen Lab report said it found "compelling evidence that the Chinese government operates the GC" [Great Cannon] despite Beijing's denials of involvement in cyberattacks.

"While the attack infrastructure is co-located with the Great Firewall, the attack was carried out by a separate offensive system, with different capabilities and design," said the report, which included collaboration from researchers at the University of California and Princeton University.

It is believed the Great Firewall programme is jointly overseen by the military, national security bureau and the propaganda ministry. The new offensive weapon was similar to one used by the United States' National Security Agency, the report said.

The new strategy could present a stumbling block to the global rise of internet giants such as Baidu and Tencent which an internet security expert source described as "victims".

Overseas consumers might grow wary of the companies if they feel Beijing is using them to help carry out censorship.

This article appeared in the South China Morning Post print edition as: 'Great Cannon' tested for a year