“ ‘The public doesn’t understand,’ (mathematician and former Sun Microsystems engineer Susan Landau) told me, speaking about so-called metadata. ‘It’s much more intrusive than content.’ She explained that the government can learn immense amounts of proprietary information by studying ‘who you call, and who they call. If you can track that, you know exactly what is happening—you don’t need the content.’
For example, she said, in the world of business, a pattern of phone calls from key executives can reveal impending corporate takeovers. Personal phone calls can also reveal sensitive medical information: ‘You can see a call to a gynecologist, and then a call to an oncologist, and then a call to close family members.’ And information from cell-phone towers can reveal the caller’s location. Metadata, she pointed out, can be so revelatory about whom reporters talk to in order to get sensitive stories that it can make more traditional tools in leak investigations, like search warrants and subpoenas, look quaint. ‘You can see the sources,’ she said. When the F.B.I. obtains such records from news agencies, the Attorney General is required to sign off on each invasion of privacy. When the N.S.A. sweeps up millions of records a minute, it’s unclear if any such brakes are applied.
Metadata, Landau noted, can also reveal sensitive political information, showing, for instance, if opposition leaders are meeting, who is involved, where they gather, and for how long. Such data can reveal, too, who is romantically involved with whom, by tracking the locations of cell phones at night.
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