Google says all victims have been notified and their accounts have been secured.
The attacks announced Wednesday on Google's blog aren't believed to be tied to a more sophisticated assault originating from China in late 2009 and early last year. That intrusion targeted the Google's own security systems and triggered a high-profile battle with China's Communist government over online censorship.
The tensions escalated amid reports that the Chinese government had at least an indirect hand in the hacking attacks, a possibility that Google didn't rule out.
In the latest incident, Google believes Chinese hackers tricked people into sharing their passwords in so-called "phishing" scams.
Google said this latest probe "appears to originate from Jinan, China." That's the home city of a vocational school whose computers were linked to the assault more than a year ago on Google's computer systems, along with those of more than 20 other U.S. companies. That break-in prompted Google to move its Chinese-language search engine from mainland China so it wouldn't have to edit its results to conform with the ruling party's censorship rules. The search engine is now based in Hong Kong, which has less stringent rules.
Google said the hacks targeted top U.S. government officials as well as Chinese political activists. Google wouldn't say what parts of the U.S. government were targeted or whether any confidential information may have been contained in the breached Gmail accounts. However, the company's statement said the attacks also included officials in South Korea as well as (unnamed) other Asian countries military personnel and journalists.
"The goal of this effort seems to have been to monitor the contents of these users' emails, with the perpetrators apparently using stolen passwords to change peoples' forwarding and delegation settings," Google said.
Coincidentally, the disclosure of the hack came just a day after United States warned that it would retaliate against a cyber attack as if it were a real-world instance of military aggression.