iPhone apps are spying on you, here are the most dangerous ones

A new report reveals that the Fitbit app can track you even when you're not exercising.

If you own a smartwatch or use other devices to track your physical activity, you probably have one or two fitness apps on your smartphone. They can be useful for logging your runs, weight training, or cycling, but according to a new study from VPN company Surfshark, some of these apps may be collecting more personal data than you think.

Surfshark analyzed 16 popular iPhone fitness apps through Apple App Store data and found that they, on average, collect 12 different types of data out of the 35 types that Apple says apps can collect.

“Out of 16 fitness apps, 75% of them share user data with third parties,” Surfshark said.

“This process is called 'tracking', where data collected by the app about a specific user or device – such as user ID, device ID or profiles – is linked to data from third parties.”

The most data-hungry was Fitbit, which was found to collect up to 24 types of data, 19 of which were not necessary for the app to function. Surfshark explained that this additional data could be used for third-party advertising, developer marketing, analytics, or product personalization.

Although Fitbit collects more data, Strava, the social fitness app, uses more data outside of the app's functionality, with 21 types of data, which is also the total number it collects.

“Some apps collect double or nearly double the average amount of data. For example, Fitbit collects up to 24 unique types of data, making it the most data-hungry app,” Surfshark said.

Centr stands out as the app that reports collecting only three types of data: user ID, product interactions, and error data. However, one of these is used for tracking. By comparison, Fitbit collects about 8 times more data.

Other apps that collect a lot of personal data include Nike Training Club, Runna, The Body Coach Workout Planner, and ALO Wellness Club. Nike's app uses sensitive personal data to target users with ads, while PUSH Workout & Gym Tracker only collects seven pieces of data and doesn't use it outside of the app's functionality.

However, PUSH requires an annual subscription of £89.99, providing direct revenue. Free apps, on the other hand, rely on using your personal data to earn money from advertisers.

While you may not have consented to all of the data uses that these apps automatically share, it's concerning to see how much of it they pass on to third parties for marketing and analytics purposes.

Surfshark only analyzed usage of these apps on iPhone and iPad, so it’s not known whether Fitbit is the “worst” on Android. But this study is a reminder to always read the terms and conditions before installing apps, especially free ones.

iPhone users can also enable the 'Ask App Not To Track' option when installing a new app, preventing apps from sharing data with third parties for advertising purposes.