Passively 'Sniffing' Data How Mobile Network Spying Works

British intelligence agency GCHQ has been targeting mobile phone company networks. Telecoms security expert Philippe Langlois explains what they can find this way, and how users can protect themselves from such snooping.
British intelligence has allegedly been tapping into data from mobile phone companies.

British intelligence has allegedly been tapping into data from mobile phone companies.

ROBERT GALBRAITH/ REUTERS