Google says the warning does not necessarily mean the user's account has been hacked, but that it believes the user may be a target of phishing or malware.
This week, Google began warning a subset of its users that it believes may be the target of state-sponsored attacks.
Eric Grosse, VP of security engineering for Google, said in an official blog post on Tuesday: “We are constantly on the lookout for malicious activity on our systems, in particular attempts by third parties to log into users' accounts unauthorised.
“When we have specific intelligence – either directly from users or from our own monitoring efforts – we show clear warning signs and put in place extra roadblocks to thwart these bad actors.”
Grosse said Google is now taking this a step further with a new warning system, which will display a message at the top of the user's Gmail page. The new warning states: "We believe state-sponsored attackers may be attempting to compromise your account or computer." The message will pop up in any browser.
“If you see this warning, it does not necessarily mean that your account has been hijacked. 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,” says Grosse.
While Google cannot divulge the details of how it knows of state-sponsored activity, Grosse says its detailed analysis and victim reports “strongly suggest” the involvement of states or state-sponsored groups.
“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. And we will continue to update these notifications based on the latest information.”
Grosse advises users who may see the warning to immediately create a unique password that has a good mix of capital and lowercase letters, punctuation marks and numbers. Users are also advised to make use of the two-step verification system for their Gmail accounts.
Over the past year, Google clashed with Chinese authorities after the search giant alleged the country's government was responsible for the hacking of the Gmail accounts of a number of high-profile US officials.
The Shanghiist reports numerous journalists and activists in China have already been seeing the warning message from Google.
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