How SS7 Enables Phone Location, Tracking and Manipulation

HN cites it as the foundational demonstration that SS7 is insecure, relevant to arguments about SMS-based two-factor authentication.

Tobias Engel's 31C3 talk shows how weaknesses in the SS7 telephone signaling network let companies and attackers locate, track and manipulate phones from anywhere in the world, with precision down to about 50 meters.