NSA Can Trace People 'Through Power Lines'

A former NSA worker says spooks can pinpoint your location using power lines - but forensic experts cast doubt on the claim.

The NSA's headquarters in Maryland

An unnamed former staff member at the National Security Agency (NSA) says whistleblowers appearing on film can be traced using power lines.

Network Frequency Analysis (ENF) is usually used to prove audio and video has not been tampered with, but the source says it can be used to determine the physical location of someone.
The analysis is carried out by analysing the 50 Hertz (60 Hertz in US) energy sound generated by power grids - which is nearly inaudible.
The hum is captured by most audio recording devices, and investigators can peel away layers of audio until the bare hum remains. The hum can then be scrutinised for unusual variations.
This week, German website Heute.De reported an unnamed former NSA worker who said the agency can use the technique to determine where a recording of a TV interview or other video clip took place.
It works by comparing captured energy hums with those previously recorded across the grid.
But experts say that while in principle it could be possible, in reality it was unlikely to be practical.
Veteran ENF forensic expert Philip Harrison told The Register: "Let me start by saying that in principle it could well be possible to use ENF to determine the location a recording was made as well as the time it was made."
But he added that "hundreds or thousands of logging devices" would be needed across each country to locate a recording location accurately.
Ian Appleby, who has worked in the energy and defence sectors, was also sceptical: "You would need a tap on every one of thousands of transformers."