Intel and Nvidia are prevented by the U.S. government from selling chips to four Chinese supercomputer centers, CNNMoney reported.

According to the outlet, the computers in question are believed to be associated with "nuclear explosive activities," though details of such conclusion have not been disclosed.

The U.S. Department of Commerce reportedly claims, "The TianHe-1A and TianHe-2 supercomputers are believed to be used in nuclear explosive activities."

The four supercomputing institutions were listed in the government's ban list since February, PCWorld cited. They are found to be "acting contrary to the national security or foreign policy interests of the United States."

These include Changsha City's National University of Defense Technology, involved in building Tianhe-2 -- the world's fastest supercomputer -- and Tianhe-1A.

For those who may not know, supercomputers perform at or close to the currently-highest operational rate for computers, TechTarget described. These types of technology are predominantly used in scientific and engineering applications, which usually require gargantuan databases.

These machines also have the ability to create "precise models of complex environments," such as simulating weather and nuclear explosions, CNNMoney noted.

The National Supercomputing Center of Guangzhou is also operating the Tianhe-2, PCWorld said.

Designers for the computer claimed that it is used for scientific studies (such as genome research), Tom's Hardware wrote. The machine is reportedly using mainstream server chips from Intel.

As told by CNNMoney, China has approximately 250 nuclear warheads, while the United States had 1,642. Russia, on the other hand, is said to own 1,643.

In other news, China is speculated to man the recent attacks on Github and internet freedom group Great Fire TechCrunch reported. A concrete evidence, reportedly, is already available, and Citizen Lab is credited for its discovery.

As told by TechCrunch, Citizen Lab has looked into the attacks, identifying the so-called "Great Cannon." This is said to be a tool that intercepts and redirects data to "specific sites."

Citizen Lab reveals, "The attack launched by the Great Cannon appears relatively obvious and coarse: a denial-of-service attack on services objectionable to the Chinese government."

"Yet the attack itself indicates a far more significant capability: an ability to 'exploit by IP address.' This possibility, not yet observed but a feature of its architecture, represents a potent cyberattack capability," the report went on.

Interestingly, Citizen Lab cited two other instances of government-tampering with unencrypted Internet traffic. These include the use of QUANTUM by the U.S. NSA and U.K.'s GCHQ.

For more information about supercomputers, check out the following videos.