The new attacks come as Beijing has increased censorship in China, and grown more vocal about how the Internet should be governed globally. In a number of recent public appearances, China’s Internet czar, Lu Wei, has called for respect for China’s Internet sovereignty, meaning that China should have the right to manage the Internet within its borders as it wants.

But the GreatFire.org material on GitHub, which is based in San Francisco, offers an unusual exception. By offering code that unblocks sites within China, it is assumed to be violating Chinese laws from abroad. James Andrew Lewis, a senior fellow at the Center for Strategic and International Studies, said the attack was an attempt to deal with extraterritoriality on the Internet.

“China is trying to redefine the rules of the Internet and they’re feeling their way forward as they do it,” he said. “This is one of another set of actions to say China will have a bigger voice in how the Internet works.”

He added that the United States had reacted strongly to distributed denial of service attacks by Iran in the past, and in this case the Obama administration could increase pressure and enact stiffer penalties against China if these types of attacks continue.

If the style of the most recent wave of attacks is well known, novel elements present major difficulties for those seeking to keep the site up, according to a number of security experts. In particular, because the traffic comes from real users scattered across the globe, instead of a concentrated network of infected computers, it is hard to sort the real traffic from the fake.

Experts said they could not be certain who was behind the attacks. But it appears that signals to or from Baidu ads and analytics tools are being redirected toward the targeted sites when users outside China visit a site inside China. Because the signals seem to be diverted at the gateway between China and the rest of the world, analysts suspect the government and the Great Firewall.

In a post on a security website run by Insight Labs, an analyst wrote that “a certain device at the border of China’s inner network and the Internet has hijacked” connections going into China.