Starting today, Facebook will use data from its users for their new ad network, Atlas, which will serve up ads on non-Facebook sites based on what Facebook knows about you.

Which is good news for advertisers, and not so good news for users concerned about their personal privacy.

Different from Audience Network, a mobile ad network Facebook introduced in April, Atlas is a sort of alternative to Google’s AdWords, which will let advertisers follow users across the web and mobile devices.

Erik Johnson, head of Atlas, wrote in a blog post that the network addresses a major limitation of cookies, the industry’s vehicle for tracking users and serving ads on desktop. “Cookies don’t work on mobile, are becoming less accurate in demographic targeting and can’t easily or accurately measure the customer purchase funnel across browsers and devices or into the offline world,” The blog presents Atlas as the solution since it uses “people-based marketing.”

While the move might discomfit some users who are suspicious about how Facebook employs their personal data, it presents a new option for advertisers and an alternative to Google.