"the newly founded Department of Homeland Security began inviting computer companies to develop intelligent systems that could "mine" data on individuals, whizzing round state, private and public databases to establish what kind of person was buying the ticket.

In 2003, one of the pioneers of the system, speaking anonymously, told me that the project, by now called Capps II, was being designed to designate travellers as green, amber or red risks. Green would be an individual with no criminal record - a US citizen, perhaps, who had a steady job and a settled home, was a frequent flyer and so on. Amber would be someone who had not provided enough information to confirm all of this and who might be stopped at US Immigration and asked to provide clearer proof of ID. Red would be someone who might be linked to an ever-growing list of suspected terrorists - or someone whose name matched such a suspect.

"If you are an American who has volunteered lots of details proving that you are who you say you are, that you have a stable home, live in a community, aren't a criminal, [Capps II] will flag you up as green and you will be automatically allowed on to your flight," the pioneer told me."
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Incidentally, I complained about being singled out unusually often to the screener - they offered to let me fill out a form that would result in a background search and maybe get me onto a green list. I declined.