Google has begun issuing in-browser warnings to users it believes are being spied on by government authorities.
A red banner reading, "Warning: We believe state-sponsored attackers may be attempting to compromise your account or computer" will now appear when users who Google believes are being attacked log into their Gmail accounts.
"If you see this warning it does not necessarily mean that your account has been hijacked," said Google's vice president of security engineering, Eric Grosse, on Google's Online Security blog.
"It just means that we believe you may be a target, of phishing or malware for example, and that you should take immediate steps to secure your account."
However, Grosse's blog goes on to say: "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."
The mysterious statement comes after a series of security concerns for Google in the past couple of years.
Accusations of mining unencrypted Wi-Fi data in Google Streetview "wardriving" exercises helped to stir up a general public mistrust surrounding the vast amount of data the search engine giant possesses on its users.
In 2010, Google cited a "highly sophisticated and targeted attack" from China as a major contributing factor to its decision to remove availability of Google – and give up its attempts to stop the Chinese government censoring search results – in the country.
The company's March 2012 hiring of ex-DARPA director Regina Dugan lends credence to the idea that Google is working with intelligence agencies, which may in turn explain why it cannot "go into details" about its new snooping alert service.
"We believe it is our duty to be proactive in notifying users about attacks or potential attacks so that they can take action to protect their information," said Grosse. "And we will continue to update these notifications based on the latest information."