The AccuWeather app has been updated so it no longer shares location data of people who had opted out of revealing where they were.
A security researcher found that the app shared location data even when users opted out.
The app collected information that was passed to another firm to target ads.
In a statement, AccuWeather said it took privacy "seriously" and often went beyond basic legal requirements to protect its users.
The popular app is used by tens of millions of people to get local forecasts of weather conditions. It is available for both Apple and Android phones.
Security researcher Will Strafach found that the iOS version of the app regularly sent detailed information about the wi-fi router it used to a firm called Reveal Mobile.
The location-based data was gathered and shared even when people said they did not want to share GPS information.
While the wi-fi data was "less precise" than GPS it was still useful to marketers, he said.
Reveal maintains a database of which wi-fi router is located where and, said Mr Strafach, uses it to map the day-to-day movements of users. The data built up about travel habits and routines was then given to ad firms looking for lifestyle information.
In a statement given to tech news site ZDNet, AccuWeather said it had only just started working with Reveal Mobile and planned to use the data it gathered to get a better idea of who its users were.
It said it sought to have its terms and conditions keep up with current laws surrounding data privacy and location sharing.
In a further statement, it said it planned to update the app to ensure "zero data" was sent to Reveal Mobile if users opted out of location sharing.