Google has begun routinely encrypting Web searches conducted in China, posing a bold new challenge to that nation's powerful system for censoring the Internet and tracking what individual users are viewing online.

The company says the move is part of a global expansion of privacy technology designed to thwart surveillance by government intelligence agencies, police and hackers who, with widely available tools, can view emails, search queries and video chats when that content is unprotected.

China's Great Firewall, as its censorship system is known, has long intercepted searches for information it deemed politically sensitive. Google's growing use of encryption there means that government monitors are unable to detect when users search for sensitive terms, such as "Dalai Lama" or "Tiananmen Square," because the encryption makes them appear as indecipherable strings of numbers and letters.

China - and other nations, such as Saudi Arabia and Vietnam, that censor the Internet on a national level - will still have the option of blocking Google search services altogether. But governments will have more difficulty filtering content for specific search terms. They also will have more trouble identifying which people are searching for information on sensitive subjects, experts say.

The development is the latest - and perhaps most unexpected - consequence of Edward Snowden's release last year of National Security Agency documents detailing the extent of government surveillance of the Internet. Google and other technology companies responded with major new investments in encryption worldwide.

Chinese officials did not respond to questions about Google's decision to routinely encrypt searches there, but the move threatens to ratchet up longstanding tensions between the American tech powerhouse and the government of the world's most populous nation.

"No matter what the cause is, this will help Chinese netizens to access information they've never seen before," said Percy Alpha, the co-founder of GreatFire.org, an activist group that monitors China's Great Firewall. "It will be a huge headache for Chinese censorship authorities. We hope other companies will follow Google to make encryption by default."

Alpha, who like other members of the group uses a pseudonym to evade Chinese authorities, noted that Google began encrypting searches in the country more than two months after GreatFire.org publicly challenged the company to do so in an opinion piece published by Britain's Guardian newspaper in November.

That piece came in response to a speech by Google's executive chairman, Eric Schmidt, in which he said, "We can end government censorship in a decade" through expanding encryption. GreatFire.org said the company didn't need to wait 10 years; it could encrypt all searches in China far more quickly.

Google denied that the group's agitation had anything to do with the rollout of encryption technology in China, saying that it began in February for unrelated reasons. All searches made from most modern browsers will be encrypted in the coming months. The completion date for the worldwide rollout is not yet clear, the company said.

"The revelations of this past summer underscored our need to strengthen our networks. Among the many improvements we've made in recent months is to encrypt Google search by default around the world," spokeswoman Niki Christoff said in an emailed statement. "This builds on our work over the past few years to increase the number of our services that are encrypted by default and encourage the industry to adopt stronger security standards. "

Google largely pulled out of mainland China in 2010, moving many of its operations to the quasi-autonomous base of Hong Kong after refusing to comply with orders to censor searches or redirect them to preferred sites - something that competitors who remained behind still do.

Since then, the company's share of the search market in China has dwindled to as low as 5 percent, according to Beijing-based market-research firm Marbridge Consulting. The vast majority of Internet users there use the Chinese search engine Baidu, even on phones running Google's Android operating system.

This means that the effect of Google's increased use of encryption could be limited in its reach since those who use Google in China - typically tech-savvy and young - often already know ways past the Great Firewall.

"Those who are technically sophisticated don't really need another tool to get around censorship," said Jason Ng, author of "Blocked on Weibo: What Gets Suppressed on China's Version of Twitter (and Why)."

Google began offering encrypted search as an option for some users in 2010 and made the protection automatic for many users in the United States in 2012. The company began encrypting traffic between its data centers after The Washington Post and The Guardian, relying on documents provided by Snowden, reported last year on the massive extent of Internet spying by the National Security Agency and its allies. Microsoft and Yahoo soon followed with similar initiatives.

Encrypted search has come more slowly in other parts of the world, and especially to those using older browsers. Firefox, Safari and Google's own Chrome browser support automatic encryption, but older generations of Microsoft's Internet Explorer - still popular in China and much of the world - do not. Internet Explorer 6, which was first released in 2001 and does not support encrypted Google searches, is used for 16 percent of Chinese Internet traffic, according to NetMarketShare.com, which tracks usage.

The move to routine encryption could spark backlash from Chinese authorities, who constantly tweak their Great Firewall to block the flow of unwanted content and also to maintain the ability to monitor Internet users in China.

"The Great Firewall is entirely a moving target," said Richard Clayton, a computer security researcher for the University of Cambridge, in England, who has studied Chinese Internet filtering. "They are tweaking it all the time."

The censorship poses an obstacle to Chinese businesses that are trying to expand internationally because they lack reliable access to sites with global audiences, such as Facebook. It can be hard to determine what the government will block on any given day.

"In China, a lot of things are like this," said Jiang Tao, founder of CSDN, a Chinese software developer community. "You don't know what you can do, what you can't do. No one tells you."

Google's growing use of encryption could prompt China to block Google searches altogether or even all services offered by the company. Though Google has a much smaller market share in China than elsewhere in the world, it is still widely used by international firms and some others, meaning there could be economic consequences to an outright block.

Another option would be what experts call a "man-in-the-middle attack" that would allow Chinese censors to intercept encrypted traffic and decode it before it reaches Google servers. For many users, such an attack would be obvious because their browsers would warn that the communication had been accessed before reaching its intended recipient. Users would be free to proceed with the query, even in the face of a man-in-the-middle attack, but the protection offered by Google's encryption would be lost.

Privacy advocates, who long have criticized Google, said its expanded use of encryption will do nothing to curb the company's own tracking of the website visits, emails and search queries of its users. Such information helps the company target advertising, the key source of revenue for the company.

"It's a good move to encrypt as much as possible, but I really think Google is grandstanding here," said Jeff Chester, executive director of the Center for Digital Democracy, an advocacy group based in Washington.

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