I first heard this story on the Search Engine podcast and had to read the book for myself. Joseph Cox chronicles in "Dark Wire" the story of how the FBI secretly ran a phone company for criminals, resulting in a record number of arrests of drug criminals and organized crime. I've recently fallen down a rabbit hole with personal cyber security and privacy, so it was fascinating to hear how something as trustworthy as an encrypted phone could be used to spy on criminals. It makes you think!