The Wall Street Journal thinks Edward Snowden may have provided China with a powerful new cyberweapon.

China is known for its so-called Great Firewall, a nationwide system of web blocks and filters that the government uses to maintain strict online censorship in mainland China.

Now it reportedly has a complementary offensive tool — called the Great Cannon — to go after sites it doesn't like.

And, The Journal emphasizes, the cyberweapon's code looks similar to an NSA program that the former NSA contractor took from US systems and released to journalists.

"The Great Cannon is not simply an extension of the Great Firewall," experts at the University of Toronto's Citizen Lab said, "but a distinct attack tool that hijacks traffic to (or presumably from) individual IP addresses and can arbitrarily replace unencrypted content as a man-in-the-middle."

China can now reroute innocent traffic coming to Chinese websites and use it for a malicious distributed denial of service (DDoS) attack to overload the servers of another website. It may also be able to inject malicious code into target computers.

This diagram shows how China's "Great Cannon" works with its "Great Firewall" to hijack traffic and attack websites. CitizensLab

Citizen Lab notes that the only other "known instances of governments tampering with unencrypted internet traffic to control information or launch attacks" involve the use of a program called Quantum that was developed by the US' National Security Agency (NSA) and the UK's Government Communications Headquarters (GCHQ).

Snowden revealed the existence of Quantum through slides given to American journalists Glenn Greenwald and Laura Poitras in Hong Kong after he arrived on May 20, 2013. The Journal is now wondering whether the former NSA contractor provided the source code to Beijing before flying to Moscow on June 23.

"Did Snowden give the Chinese the code for the Great Cannon?" its editorial asks. "He denies sharing anything with foreign governments. But then he's an admitted liar, and we don't know what the Chinese and Russian spy services have been able to copy from what he stole."

A monitor broadcasts news on the charges against Edward Snowden, a former contractor at the National Security Agency (NSA), by the United States, at a shopping mall in Hong Kong June 22, 2013. REUTERS/Bobby Yip

The Journal's evidence regarding Snowden and the Great Cannon is scant and circumstantial and based mainly on suspicion of Snowden, the similarities between the Great Cannon and Quantum, and timing.

"A South China Morning Post report that the Great Cannon has been under development for about a year is suggestive," The Journal asserts. "This means China's hacking bureaucracy geared up to produce this new product soon after the Snowden leaks."

In any case, China now has a powerful new cyberweapon to enforce its status as the world's vastest internet-censorship regime.

"The operational deployment of the Great Cannon represents a significant escalation in state-level information control: the normalization of widespread use of an attack tool to enforce censorship by weaponizing users," Citizen Lab notes.