An investigation by the New York Times has revealed the sheer scale of how our location is tracked by apps on our smartphones.

The findings: Several businesses claim they can track about half the mobile devices in the US, with precise locations updated up to 14,000 times a day in some cases. This data is sold or analyzed for advertising and retail, among other uses. Sales of location-targeted advertising reached an estimated $21 billion this year, and it’s a growing market. The data is anonymized, but those with access to the raw data could easily identify someone without consent. Companies aren’t content with just tracking your location, either—they want to predict your future movements too, as this patent from Facebook shows.

Old news? Most of us know our phones collect location data. But by clarifying the sheer scale, monetization, and risk of identification, the NYT is making it a lot harder to ignore the issue.

What you can do: If this all sounds terrifying, don’t panic. A solution is within reach. You’ll need to carefully comb your phone’s settings and permissions. The NYT provides a handy guide here, but if you want a simple rule of thumb: delete free apps.