How US Customs combats illegal drug trade
31 July 2014 Last updated at 17:00 BST
The number of listings offering illegal drugs for sale on the "dark net" appears to have more than doubled in less than a year, BBC News has learned.
The US Federal Bureau of Investigation (FBI) closed down the original online illegal drug market, Silk Road, in 2013.
But new figures suggest the trade has actually increased since then.
And other research indicates one in four British drug users has accessed hidden websites.
Christian Crawford, Supervisor, US Customs and Border Protection showed the BBC's Angus Crawford around the postal facility in Los Angeles where US Customs try to halt the flow of illegal drugs coming into and out of the United States.
Camera/editing: Tony Smith