The full fury of the Internet attack started three hours before polls opened. As people in Hong Kong prepared to cast electronic ballots in an effort to show Chinese authorities their hunger for democracy, hackers opened fire with a potent effort to derail the vote.

Suddenly, a flood of data swarmed the servers designed to handle the voting in a poll held by Occupy Central with Love and Peace, a burgeoning protest movement that has sought the right for Hong Kong people to nominate and elect their own chief executive, the territory's most powerful position.

But the informal vote on universal suffrage was attacked by at least 300 gigabits of data per second – and perhaps as high as 600, a level not before reached in a publicly disclosed hacking attack. The torrent reached 200 million packets, or tiny bits of data, per second. It was "just a stunning amount of traffic," said Matthew Prince, chief executive officer of CloudFlare, the San Francisco-based Internet security company that managed to keep the website online.

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The number of packets they had to parry was huge, "within an order of magnitude of what Google has to deal with in its entire infrastructure."

And it wasn't just once. As hundreds of thousands of people in Hong Kong sought to use the informal poll to register their displeasure with China's rule, the volume of packets hit 200 million per second "easily a dozen times" over the weekend, continuing into Monday in Hong Kong, Mr. Prince said.

It was, he believes, the biggest and most sophisticated hacking attack of its kind.

But the size of the attack was matched by the size of the turnout. Observers thought perhaps 290,000 and 350,000 people might turn out.

But by Monday at 2 p.m., 716,775 people had cast ballots, roughly 20 per cent of those eligible – and voting will remain open for nearly another week. Though voting opened Friday, votes were still pouring in at a rate of 1,300 per hour Monday.

Edward Chin, a hedge fund manager who has led the efforts to fund the movement, called it a repudiation of Beijing, which two weeks ago issued a white paper that baldly asserted China's sovereignty over Hong Kong. On Friday, China's powerful State Council said any effort to democratically select and elect a chief executive would be "illegal and invalid," according to the state-owned Xinhua news agency.

"The general message to Hong Kong people was, 'you better behave,' " said Edward Chin, a hedge fund manager who leads the Occupy finance committee. "But scare tactics don't really work."

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Indeed, many at polls said they had come specifically in response to Beijing's unbending position.

The turnout was particularly large given that the vote is, in strictly legal terms, futile. Decisions on Hong Kong's political future will be first shaped by the region's legislature, but ultimately decided by Beijing. The vote was run by neither of those authorities. It was, instead, meant to apply moral pressure, and offer a glimpse into the will of the people of Hong Kong.

In that sense, it has already succeeded, said Simon Young, a Hong Kong barrister and director of research in the law department at Hong Kong University.

"Even though Beijing says it's illegal or has no influence, they can't ignore it," he said. "It's potentially a game-changer. Because it means there's a lot of public support. The images of people lining up at polling stations really spoke volumes."

If nothing else, the sheer number of voters is likely to influence the Hong Kong legislature's willingness to support alternative measures, such as offering people the chance to recommend – if not outright nominate – leaders, Mr. Young said.

China and its supporters, however, sought to undermine the vote. Robert Chow, who has led a "Silent Majority" group opposed to the Occupy movement, said the number of ballots looked "manufactured." And, he said, Beijing should feel no more obligated to give in to Hong Kong's malcontents than Washington might listen to "people in the Middle East saying they want America to burn."

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"How can a government openly accept, under duress, an unconstitutional type of reform, just because there's a hue and cry from a group of people?" he said.

On Monday, the Global Times, the sharp-tongued tabloid owned by China's Communist Party, offered its own stinging riposte. In an editorial, the paper said "Beijing will never compromise on sovereignty-related issues." The editorial took special umbrage at the electronic poll, saying "this 'invention' is tinged with mincing ludicrousness."

But the brushoff was set against the massive hacking attack, which observers said bore some of the hallmarks of a sophisticated state-run operation. The U.S. government and American security firms have accused the Chinese military of running units dedicated to global hacking. And "clearly the Chinese government has a very obvious motivation for the target," said Ian Brown, associate director of Oxford University's Cyber Security Centre.

"It's not trivial to develop the software to launch the kind of attacks you're talking about," he said.

The Occupy hacking attack originated from computers in 180 different countries, and the hackers were "doing some really clever things," said Mr. Prince. For example, they targeted a little-used cryptography tool that requires significant computational horsepower, in hopes of bringing the voting system to a halt.

If the Chinese are behind the hacking, "it shows that regardless of the means, they will use everything to try to suppress the will of Hong Kong people," said Wong Yiu Chung, head of the political science department at Lingnan University in Hong Kong. Given recent statements from Chinese leadership, "I'm very pessimistic about the possibility of political reform," he said. It's more likely, he added, that Beijing will make a small concession, such as limiting the number of Hong Kong tourist visas it issues to mainland visitors.

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To others, the strong Chinese response has raised fears about what might happen if the Occupy movement, as it has long threatened, brings enough people onto the streets to shut down Hong Kong's financial district.

"There's nothing to stop China from sending troops across the border into Hong Kong," said Victor Shih, an associate professor in international relations at the University of California at San Diego.

"As we saw with Tiananmen Square, the Chinese Communist Party, when pushed hard to maintain power, will resort to almost any tactics."