Google began warning users in June that it had detected a series of attempted attacks by groups that it believed were connected with foreign governments. A Google official told the New York Times that the company has collected new information about the kinds of attacks that are coming in against its users. Security researchers have said the same thing in recent months, pointing to attacks emanating from Iran and other countries in the Middle East. Google has not disclosed how it is identifying state-sponsored attacks, but researchers have speculated that one way is by looking at the kind of techniques the attackers are using.
Source: https://threatpost.com/google-warning-about-more-state-sponsored-attacks-100412/77080/