A US Congressman has learned first-hand just how vulnerable cellphones are to eavesdropping and geographic tracking. Hackers were able to record his calls and monitor his movements using nothing more than the public ten-digit phone number associated with the handset he used. The hack was done by accessing Signalling System No. 7, or SS7, a telephony signalling language used by more than 800 telecommunication companies around the world. The problem with SS7 is that it’s only as secure as its least secure or trust-worthy member.”]