Still, the Chinese program illustrates how far officials in Beijing are willing to go to censor Internet content they deem hostile. “This is just one part of President Xi Jinping’s push to gain tighter control over the Internet and remove any challenges to the party,” said James A. Lewis, a security expert at the Center for Strategic Studies in Washington.

Image Bill Marczak, right, a co-author of the report on a powerful new Chinese cyberweapon, with Morgan Marquis-Boire, a fellow Citizen Lab researcher. Credit Thor Swift for The New York Times

Beijing continues to increase its censorship efforts under its State Internet Information Office, an office created under Mr. Xi to gain tighter control over the Internet within the country and to clamp down on online activism. In a series of recent statements, Lu Wei, China’s Internet czar, has called on the international community to respect China’s Internet policies.

Sarah McKune, a senior legal adviser at the Citizen Lab at the Munk School of Global Affairs at the University of Toronto and a co-author of the report, said, “The position of the Chinese government is that efforts to serve what it views as hostile content inside China’s borders is a hostile and provocative act that is a threat to its regime stability and ultimately its national security.”

The attacks also show the extent to which Beijing is willing to sacrifice other national goals, even economic ones, in the name of censorship. Baidu is China’s most visited site, receiving an estimated 5.2 million unique visitors from the United States in the last 30 days, according to Alexa, a web ranking service.

Kaiser Kuo, a Baidu spokesman, said that Baidu was not complicit in the attacks and that its own networks had not been breached. But by sweeping up Baidu’s would-be visitors in its attacks, researchers and foreign policy experts say, Beijing could harm the company’s reputation and market share overseas.

Beijing has recently said that it plans to help Chinese Internet companies extend their influence and customer base abroad. At a meeting of the National People’s Congress in China last month, Premier Li Keqiang announced a new “Internet Plus” action plan to “encourage the healthy development of e-commerce, industrial networks and Internet banking and to guide Internet-based companies to increase their presence in the international market.”

Yet the latest censorship offensive could become a major problem for Chinese companies looking to expand overseas. “They know one of their biggest obstacles is the perception that they are tools of the Chinese government,” Mr. Lewis said. “This is going to hurt Baidu’s chances of becoming a global competitor.”