Silk Road: Did users leave traces?
3 October 2013 Last updated at 12:43 BST
The FBI has announced the arrest of the suspected operator of the Silk Road - a clandestine online marketplace for drugs and other illegal items.
A spokeswoman said Ross William Ulbricht was arrested "without incident" by its agents at a public library in San Francisco on Tuesday.
Kate Bevan, a technology writer and broadcaster, told the Today programme's Justin Webb that the Silk Road was a kind of online market place where people could buy guns and drugs.
"When people use the internet sometimes... they don't want to be visible," she said.
First broadcast on BBC Radio 4's Today programme on Thursday 3 October 2013.