Facebook ads: we’ve all seen a million of them. While some are generic spam, many are very creepily on-target. Until now, Facebook has mostly used its massive hoard of detailed user data for itself, and to sell ads on its own site. But now the site you love to hate is finding a new way to bank on your favorite bands and brands, with a new advertising service that can let companies chase down and advertise to any specific group they want.

The service is called Atlas, the New York Times reports, and its bid for world domination starts today.

For businesses, the allure of Atlas is just how much information the target audience — that’d be Facebook users — have voluntarily dumped into it. Companies that use Atlas can slice and dice audiences into remarkably narrow, specific niches as desired. “You can slice and dice markets, like women 25 to 35 who live in the Southeast and are fans of ‘Breaking Bad,’” as an analyst explained to the Times.

It’s also a cross-platform product. That’s a fancy way of saying that because your Facebook profile is still your Facebook profile no matter what computer or iPad or phone you’re using, Facebook can track your behavior across all devices and let advertisers reach you on all of them.

The NYT points to the example of Pepsi, which is one of the first companies to sign on. If they “wanted to reach college age men with ads for its Mountain Dew Baja Blast,” the Times explains, they could use the service to “identify several million of those potential customers and show each of them a dozen ads for the soft drink on game apps, sports and video sites.” Atlas also provides metrics to companies like Pepsi so they can figure out which ads are the most effective.

Facebook announced that it was collecting user data for resale purposes back in June. Technically there are ways to opt out, but they may or may not exactly work.

Facebook’s data is increasingly valuable as users switch away from traditional desktop and laptop computers and more toward mobile (and tablet) use. The web user tracking that works on your desk doesn’t work nearly as well for advertisers on your phone, and advertising companies have had a hard time figuring out how to make money off of us all in the mobile space. But Facebook is there, watching.

“The Facebook login is most useful on mobile devices, where traditional web tracking tools like cookies and pixel tags do not work,” the NYT explains. “If a person is logged into the Facebook app on a smartphone, the company has the ability to see what other apps he or she is using and could show ads within those apps.”

So yes, to clarify: Facebook knows what apps you’re using on a phone where you are also logged into Facebook, and can then insert ads into those apps that will target you based on your laptop history and Facebook “likes.”

While this may sound fairly terrifying to ordinary data points users like you and me, advertisers and analysts see a lot of potential in the service. Facebook is now competing directly with Google, which famously scans for key words in user e-mails, web searches, and more to place targeted ads in those products.

Facebook also insists that the data is aggregated and does not include individual identifying information, which they never disclose to marketing companies. However, that doesn’t mean that a company (like Pepsi) can’t take their own list of Facebook “likes” and match it against detailed advertising info they get from Facebook to do some matching of their own.

With New Ad Platform, Facebook Opens Gates to Its Vault of User Data [New York Times]

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