Fergal Crehan dispenses simple advice to journalists when they go out to work. “Don’t take your phone”, he says. Smart phones are sieves through from data flows, compromising sources, jeopardising privacy and endangering their users, he warns. Standard fare from a tin-foil-hat-sporting conspiracy theorist. Crehan, however, is an eminent barrister, who specialises in data security, and who for many years worked for the mobile phone industry.