> U.S. officials say it remains a minuscule percentage of overall travellers — 0.007 per cent, or roughly one per 13,000. The Department of Homeland Security says it's necessary to combat crimes like terrorism and child pornography.

I'm sick of hearing this argument. Either it's a small percentage of travellers or it's necessary to combat those crimes, but you cannot have both. The only way to have both of those is if you already have some probable cause or a reason to search particular individuals, in which case there's no need for it to be warrantless.