Apple has told the various companies said to be secretly recording people's activities on their iPhones that they must stop immediately.
Developers of some of the world's biggest apps have been rumoured to be using technology to watch people as they use their phones, in contravention of Apple's guidelines.
Now Apple has said they must stop the recording, alert users to it or face "immediate action".
The statement comes after a Techcrunch investigation alleged that many of the App Stores biggest apps were using analytics tools that watched people as they used the apps and recorded them as they did so, potentially hoovering up sensitive data like credit card information as they did so.
“Protecting user privacy is paramount in the Apple ecosystem," an Apple spokesperson said. "Our App Store Review Guidelines require that apps request explicit user consent and provide a clear visual indication when recording, logging, or otherwise making a record of user activity.
“We have notified the developers that are in violation of these strict privacy terms and guidelines, and will take immediate action if necessary."
Techcrunch said that developers had been given only a day to remove the problem software and submit the apps to the store again, or face the risk of having them removed entirely.
The same analytics software is available for Android. Google's guidelines also ban such secret tracking but it is not clear if those same apps will be removed from the Play Store.