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.