Top secret documents previously provided by former NSA contractor Edward Snowden have revealed that the US and Britain broke into the network of the world's largest SIM card maker to compromise global communications. , the online news magazine founded by Snowden collaborator Glenn Greenwald, the US National Security Agency and its British counterpart, the Government Communications Headquarters , stole the encryption keys used to secure voice calls and texts from Gemalto, the largest manufacturer of SIM cards in the world.