Google believes that it can distinguish run-of-the-mill hack-attacks on Gmail accounts from state-sponsored spies trying to gain access to dissidents' email. When it detects the latter, it will display a warning for the legitimate owner to see, "We believe that state-sponsored attackers may be attempting to compromise your account or computer." The warning comes with a link to instructions for improving your password security.
You might ask how we know this activity is state-sponsored. We can't go into the details without giving away information that would be helpful to these bad actors, but our detailed analysis—as well as victim reports—strongly suggest the involvement of states or groups that are state-sponsored.