Apple has withdrawn hundreds of apps that were found to be capable of collecting users' personal data.
It is believed that around 250 apps - downloaded an estimated total of one million times - are affected, in what was said to be the first time Apple's thorough review process had been bypassed by iOS apps.
When contacted by ITV News, Apple confirmed that it had identified a "group of apps that are using a third-party advertising SDK [software development kit]".
The software, which Apple said was developed by mobile advertising provider Youmi, uses APIs to gather "private information", such as users' email addresses, which can then be routed to its company server.
"This is a violation of our security and privacy guidelines," Apple said.
"The apps using Youmi's SDK have been removed from the App Store and any new apps submitted to the App Store using this SDK will be rejected," the tech company said.
SourceDNA said it believed the developers of apps affected aren't aware of the violation, "since the SDK is delivered in binary form, obfuscated, and user info is uploaded to Youmi's server".
It added that it had sent a list of the affected apps to Apple, but did not state on its website which these were.
Apple said it was "working closely closely with developers to help them get updated versions of their apps that are safe for customers and in compliance with our guidelines back in the App Store quickly".