Yahoo email accounts of some journalists and other users whose work relates to China were compromised in an attack discovered this week, days after Google announced it would move its Chinese-language search services out of China due to censorship concerns.
Some journalists in China and Taiwan found they were unable to access their accounts beginning March 25, among them Kathleen McLaughlin, a freelance journalist in Beijing. Her access was restored on Wednesday, she told Reuters.
Andrew Jacobs of the New York Times in Beijing said his Yahoo Plus account had been set, without his knowledge, to forward to another, unknown, account.
In late 2009 and early this year, several human rights activists and journalists whose work related to China had similarly discovered their Gmail accounts had been set to forward to unfamiliar addresses, without their knowledge.
Google cited the Gmail attacks in January, when it announced a hacking attack on it and more than 20 other firms. Google cited those attacks and censorship concerns in its decision to move its Chinese-language search services last week to Hong Kong.
Google on Wednesday said it had identified cyber attacks aimed at silencing opposition to a Vietnamese government-led bauxite mining project involving a major Chinese firm. It said the attacks were similar to those at the heart of the company's friction with Beijing.
Yahoo did not comment on the nature of the attacks on its accounts, or whether they were co-ordinated or isolated incidents.
"Yahoo! condemns all cyber attacks regardless of origin or purpose," spokeswoman Dana Lengkeek said in an email response to a Reuters query.
"We are committed to protecting user security and privacy and we take appropriate action in the event of any kind of breach."
Google's announcement of the hacking attacks drew unprecedented outside attention to cyber-security and China's Internet controls, used to limit discussion of topics deemed sensitive or threatening to "social stability."
China's control of the Internet and media has intensified under the current leadership and reflect a lack of understanding of the Chinese public, said Hao Xiaoming, a China media expert at Wee Kim Wee School of Communication and Information in Singapore.
"China is going back rather than going forward in terms of information and control. That reflects the lack of confidence in the (current) Chinese leaders," Hao said.
"China's Internet has become a controlled Internet, an internal Internet rather than linked internationally. It defeats the whole purpose."
On Tuesday, Internet users in mainland China were sporadically unable to conduct searches through Google's portal in Hong Kong, a disruption that Google attributed to changes in China's Internet filtering configuration.
It said it did not know whether the stoppage was a technical glitch or a deliberate move in confrontations over Internet censorship.
China's Ministry of Industry and Information Technology gave no immediately reply to a request for comment on the disruption.
Google said it was monitoring the situation but it appeared the access problem had been resolved. Access has been patchy since Google shifted to Hong Kong, underscoring the vulnerability of Google's business in the world's most populous country.
Very few of the other firms mentioned by Google in January as having been affected by the attack have identified themselves.
A source at the time told Reuters that Yahoo knew it had been a target of attacks and discussed them with Google before Google went public.
Yahoo said at the time that it was "aligned" with Google's position, a statement that its Chinese partner, e-commerce giant Alibaba Group, called "reckless".
Unlike Google, Yahoo keeps some of its email servers in China. It was criticized by the Congress when it released to Chinese authorities information relating to the account of Shi Tao, a Chinese journalist who was then sentenced to 10 years in jail for revealing state secrets.