“Imagine all we could do with the data we collected!” Debbie remembered hearing at one of their early project meetings. She had kept her cool, as she always did, yes, trying to imagine all the information one could obtain by comparing itself to that of a million others. They would probably be able to forecast health events, like a heart attack or a stroke, before they happen, and it would save lives and a lot of money in emergency services and hospital costs. They would probably be able to predict the outcome of marriages, saving people from the grief of breaking up, and even act as some kind of matchmaker assistant. But neither she nor her fellow team members could have thought it would end up telling people who they were. They had controlled the questions, at first, to give (or rather sell) vital information to users, all derived from statistics also gathered from everyone. They saw it happening gradually, as users signed up on the system and volunteered their data gathered every day from …