SAN FRANCISCO - Google Inc. will stop censoring its search results in China and may pull out of the country completely after discovering that computer hackers had tricked human-rights activists into exposing their email accounts to outsiders.

The change of heart announced Tuesday heralds a major shift for the Internet's search leader, which has repeatedly said it will obey Chinese laws requiring some politically and socially sensitive issues to be blocked from search results available in other countries.

The acquiescence had outraged free-speech advocates and even some shareholders, who argued Google's co-operation with China violated the company's "don't be evil" motto.

The criticism had started to sway Google co-founder Sergey Brin, who openly expressed his misgivings about the company's presence in China.

But the tipping point didn't come until Google recently uncovered hacking attacks launched from within China. The apparent goal: gathering information about dozens of human rights activists trying to shine a light on the country's censorship and other secretive policies.

Google officials said they plan to talk to the Chinese government to determine if there is a way the company can still provide unfiltered search results in the country.

If an agreement can't be worked out, Google is prepared to leave China four years after creating a search engine bearing China's web suffix, ".cn" to put itself in a better position to profit from the world's most populous country.

"The decision to review our business operations in China has been incredibly hard, and we know that it will have potentially far-reaching consequences," David Drummond, Google's top lawyer, wrote in a Tuesday blog posting.

A spokesman for the Chinese consulate in San Francisco had no immediate comment.

Abandoning China wouldn't put a big dent in Google's earnings, although it could crimp the company's growth as the country's Internet usage continues to rise. Google, based in Mountain View, said its Chinese operations account for an "immaterial" amount of its roughly US$22 billion in annual revenue.

Although Google's search engine is the most popular worldwide, it's a distant second in China, where the homegrown Baidu.com processes more than 60 per cent of all requests.

Free-speech and human rights groups are hoping Google's about-face will spur more companies to take a similar stand.

"Google has taken a bold and difficult step for Internet freedom in support of fundamental human rights," said Leslie Harris, president of the Centre for Democracy&Technology, a civil-liberties group in Washington. "No company should be forced to operate under government threat to its core values or to the rights and safety of its users."

It's "an incredibly significant move," said Danny O'Brien, international outreach co-ordinator at the Electronic Frontier Foundation, an Internet rights group in San Francisco. "This changes the game because the question won't be 'How can we work in China?' but 'How can we create services that Chinese people can use, from outside of China?"'

Google's new stance on China was triggered by a sophisticated computer attack orchestrated from within the country. Rep. Anna Eshoo, D-Calif., praised Google for disclosing chicanery that "raises serious national security concerns."

Without providing details, Google said it and at least 20 other major companies from the Internet, financial services, technology, media and chemical industries were targeted. The heist lifted some of Google's intellectual property but didn't get any information about the users of its services, the company said.

Google has passed along what it knows so far to U.S. authorities and other affected companies.

The assault on Google appeared primarily aimed at breaking into the company's email system, "Gmail," in an attempt to pry into the accounts of human right activists protesting the Chinese government's policies.

Only two email accounts were infiltrated in these attacks, Google said, and the intruders were only able to see subject lines and the dates that the individual accounts were created. None of the content written within the body of the emails leaked out, Google said.

As part of its investigation into that incident, Google stumbled onto another scam that was more successful. Google said dozens of activists fighting the Chinese government's policies fell prey to ruses commonly known as "phishing" or malware. The victims live in the United States, Europe and China, Google said.

Phishing involves malicious emails urging the recipients to open an attachment or visit a link that they're conned into believing comes from a friend or legitimate company. Clicking on a phishing link of installs malware -- malicious software -- on to computers.

Once it's installed on a computer, malware can be used as a surveillance tool that can obtain passwords and unlock email accounts.

Google's unfettered search results won't necessarily ensure more information will be made available to the average person in China because the government could still use its own filtering tools, said Clothilde Le Coz, Washington director for Reporters Without Borders, a media watchdog group.

"The Chinese government is one of the most efficient in terms of censoring the Web," she said.