In the ad serving phase, when your computer requests an advert from the OIX (because a website has included our tag in their page), the browser sends the random number and the categories are used to deliver the targeted ad, not the details of your browsing, or anything about you or your computer.

BBC: Phorm: Your questions answered

There is, in essence, no data other than the categories and the random number stored in the system and so it's impossible to know (or indeed reverse engineer from that) who you are or where you've been.

BBC: Phorm: Your questions answered

America is now, belatedly, moving away from random screening, which led to absurdly rigorous treatment of obviously harmless categories like small children, veterans and even the planes' own pilots, to a computerised system that checks identities and assesses potential risk.

ECONOMIST: Disasters