"We would go into villages and enrol people into this biometric data system," US Marine Special Operations Command veteran Peter Kiernan recalls. "You had a device about 12 inches by six inches wide. It would scan their fingerprints, it would scan their retina, it would also take a picture of them." A United Nations document recently seen by the BBC says the Taliban are intensifying their hunt for people who worked for, and collaborated with, Nato and US forces. And the giant stores of biometric data collected by both the US military and the Afghan government could, some argue, pose...