Google Latitude (click for larger image)

Google's new Latitude location-sharing service "could be a gift to stalkers, prying employers, jealous partners, and obsessive friends," Privacy International warned Thursday.

Google introduced Latitude on Wednesday. It's a new Google Maps feature that lets users share location data with friends, using either a mobile phone or Google Gears-equipped computer.

Google knows well that it has a privacy problem, exemplified by its quixotic campaign last summer to avoid adding a link on its home page to its privacy policy. It uses sensitive data to make its products better and to figure out how to personalize ads and search. Too much privacy threatens Google's business model. Its competitors know this, too, which is why Microsoft and Yahoo have been engaged in a game of data-retention one-upmanship.

To dispel anticipated privacy concerns, Vic Gundotra, VP of engineering on Google's mobile team, tried to reassure potential Latitude users that Google designed the service so that users are in control. "Fun aside, we recognize the sensitivity of location data, so we've built fine-grained privacy controls right into the application," he said. "Everything about Latitude is opt-in. You not only control exactly who gets to see your location, but you also decide the location that they see."

Nonetheless, Privacy International said it had identified "a major security flaw in Google's global phone tracking system." The group's choice of such sinister terminology -- "phone tracking" sounds scarier than "location sharing" -- to describe Latitude hints at its history of antagonism with Google. In 2007, Simon Davies, director of the organization, wrote an open letter to Google CEO Eric Schmidt accusing the company of spreading rumors that the group was in the pocket of Microsoft and demanding an apology.

In the letter, Davies denies that Privacy International has a vested interest in attacking Google and says that the group has been critical of Microsoft, Amazon.com, and eBay, too. He speculates that Google's disparagement of his organization arose from its poor ranking in the group's 2007 Internet privacy survey.

Privacy International concedes that Google had made some effort to address privacy concerns. But it considers these safeguards useless "if Latitude could be enabled by a second party without a user's knowledge or consent."

As the organization puts it, the "danger arises when a second party can gain physical access to a user's phone and enable Latitude without the owner's knowledge."