According to researchers at GlobalWebIndex, less and less people are using Facebook. The research firm’s study found that the average Internet user in 2013 had 4.7 social media accounts, while the average user in 2014 has 5.2. Even though that would seem to be bad news for Facebook and its advertisers, it isn’t; the site can still track users all across the web (and even offline) and determine what they’re buying. How? Facebook Login.

The feature, first launched in 2008, is the preferred app sign-in method for 44 percent of users. Facebook can track the information of any user that signs into an app using Facebook Login, and as many users move away from desktop browsing entirely, that means a massive amount of information and power for Facebook.

“From an advertising point of view, [less engagement on Facebook] is not necessarily a problem, especially now with the direction Facebook is going,” GlobalWebIndex CEO Tom Smith told Forbes. ”You can target Facebook users across apps and you’re not targeting a specific application but that user anywhere they’re online.”

When it comes to mobile advertising, Facebook was so far ahead of the curve as to be laughable; Twitter, for instance, is only now launching its own login system. Is it creepy that Facebook can follow you no matter what you do across the web? No doubt. But it’s an undeniably effective way to find out what, and how, to sell to users.