A very small proportion of websites use sophisticated anonymity systems, which allow their operators to conceal their identity if they wish to. This part of the web is commonly referred to as the darknet. The darknet helps citizens to protect their security and privacy and to circumvent censorship. It also facilitate organised crime, such as the billion dollar drug market known as Silk Road. This POSTnote discusses the challenge of preventing such crimes without compromising the other uses of anonymity technologies.