The US National Security Agency may have a capability to track targets using disposable phones to evade wiretaps, documents obtained by the Electronic Frontier Foundation revealed.
The potential capability was discussed in a statement by NSA director General Keith Alexander in documents disclosed following an EFF lawsuit and raised in analysis by CATO Institute privacy research fellow Julian Sanchez.
Documents said an unnamed NSA tool had helped analysts identify phone numbers by providing generic information from the agency's signals intelligence databases.
That information contained data on a queried phone number including the total number of all calls made; the dates of the first and last calls; the number of times other unique phone numbers had called it, and the ratio of all calls to unique contacts.
Agents seeking the information did not get a list of numbers which were contacted by the phone number under investigation nor a list of those NSA databases that were queried to produce the data.
"The number of unique contacts and call/contact ratio would act as a kind of rough fingerprint— you’d assume a phone being used for dedicated clandestine purposes to be fairly consistent on that score — while the first/last call dates help build a timeline: You’re looking for a series of phones that are used for a standard amount of time, and then go dead just as the next phone goes online."