The firm's security experts, including an Indian, are set to publish their findings next month, the Daily Mail reported.
In the official company blog, Google Vice President Security (Engineering) Eric Grosse said, "We are constantly on the lookout for malicious activity on our systems, in particular attempts by third parties to log into users' accounts unauthorised. Today, we are taking that a step further for a subset of our users, who we believe may be the target of state-sponsored attacks".