Posted to an internal blog, Apple said that in 2017, 29 leakers were caught and 12 of those people were arrested.
Apple mentioned specific leaks in the memo. Earlier this year where the company told software engineers that some features planned for iOS 12 would be delayed to better focus on quality.
Another leak mentioned was the release of the final iOS 11 version that provided a treasure trove of information about the iPhone X and Apple Watch Series 3 before their release
Apple mentioned that along with criminal charges, leakers can face other legal action.
You can read the entire lengthy memo in the Bloomberg report.