Good news for advertisers, but maybe not-so-great news for users concerned about their personal data: Starting Monday, Facebook will use data it gleans from users for its new ad network, Atlas, which it will serve up ads on non-Facebook sites based on what Facebook knows about you.

Atlas is a former Microsoft property that Facebook bought last year for around $100 million that Facebook has now rebuilt from the ground up. Atlas is distinct from Audience Network, a mobile ad network Facebook introduced in April that was aimed at app developers.

See also: 16 Creepiest Targeted Facebook Ads

In contrast, Atlas is a sort of alternative to Google's AdWords, which will let advertisers follow users across the web and mobile devices. For instance, Atlas advertiser Pepsi could use Atlas to advertise one of its products on a sports site or a game app that is unaffiliated with Facebook.

In a blog post announcing the new network, Erik Johnson, head of Atlas, wrote 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," he wrote. 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. The pitch would be even more intriguing if Twitter joins the network. Re/code reports that Facebook has talked to Twitter about such a move and "the idea remains a possibility."