Since July 2008, Gmail has included a "Last account activity" link below users' inboxes that provides information about when the account was last accessed and the IP address used. But the placement of the link makes it useful mainly to people seeking to confirm an existing suspicion.
The new notification will take the form of "a very big warning," said Google product manager Will Cathcart in a phone interview.
Such a warning no doubt would have been useful to identify the attempts to access the accounts of Gmail-using human rights advocates late last year, part of the "Operation Aurora" attacks on Google's infrastructure that led it to shut down its search engine in mainland China.
"The idea behind the feature is that we already give users an idea about the activity on their account, but we wanted to provide more information," Cathcart said. "We look the login history for an account, specific to each user, and look for changes in that history based on a number of different algorithms."
As an example, Cathcart suggests, a Gmail user in the U.S. whose account was accessed from Nigeria would be shown a notification saying, "Warning: We believe your account was last accessed from Nigeria."
This wouldn't necessarily happen, however, if the user regularly traveled to Nigeria and logged into Gmail from there.
"When we think something bad is going on, we're going to make it very, very prominent," said Cathcart.
It will then be up to the user to visit the recent account activity details page to determine whether further action, like a password change, might be required.
In a blog post, Google engineering director Pavni Diwanji explains that Google does not have the capability to identify the specific location of login attempts. However, it may be possible to link the IP address of the suspicious activity with a specific location or individual.