https://www.vice.com/en_us/article/3aza95/how-police-took-over-encrochat-hacked

Something wasn't right. Starting earlier this year, police kept arresting associates of Mark, a UK-based alleged drug dealer. Mark took the security of his operation seriously, with the gang using code names to discuss business on custom, encrypted phones made by a company called Encrochat. For legal reasons, Motherboard is referring to Mark using a pseudonym.

Because the messages were encrypted on the devices themselves, police couldn't tap the group's phones or intercept messages as authorities normally would. On Encrochat, criminals spoke openly and negotiated their deals in granular detail, with price lists, names of customers, and explicit references to the large quantities of drugs they sold, according to documents obtained by Motherboard from sources in and around the criminal world.