Last weekend a company called Strava, a social network for people who want to track their workouts, updated an online map showing the routes of 1 billion workouts in 2017.

But in doing so, it seems to have exposed secret US military bases in Turkey, Syria, and Yemen.

In November, Strava announced a huge update to its global heat map of user activity that displays 1 billion activities—including running and cycling routes—undertaken by its users wearing Fitbits or other wearable fitness trackers. Security experts quickly connected the dots between user activity and known bases or locations of US military or intelligence operations.

Certain analysts have suggested the data could reveal individual Strava users by name. But in addition, potential adversaries may learn “patterns of life,” by tracking and identifying military or intelligence agency personnel, underscoring the increasing challenges of secret keeping in a digital world.