21/11/2013 06:09 GMT | Updated 25/01/2014 16:01 GMT

Follow the Money

Follow the money; an old investigative adage that says the money trail will ultimately lead to those at the heart of a crime. However, does this hold for all crimes? Particularly those online or those possessed of an extremely skewed value system.

Last week it was announced that a large-scale child sexual abuse investigation has led to the rescue of 386 young children around the world and the arrest of over 300 people. The investigation reportedly began with a Toronto man accused of running Avozfilms, a company that distributed child sexual abuse (CSA) videos to the tune of $4million in revenue.

Police say was a sophisticated site. Clients could browse Top 10 lists and reviews by other customers. There was a searchable catalogue, so those who knew what they wanted could go right to the desired title and, of course, credit-card payments were accepted.

By following the money, investigators were able to find and arrest over 300 individuals who are alleged to have bought and viewed this material. However, for the vast majority of cases, money is not the only currency at play in CSA crimes.

Last month The European Cybercrime Centre (EC3) and the European Financial Coalition against the Commercial Sexual Exploitation of Children Online (EFC) released a study into the commercial structures behind child sexual abuse. This report showed that the vast majority of child abuse material continues to be distributed for 'free' on the open net. An average of 10.1 per cent of child abuse material is distributed commercially and eight top-level distributors were responsible for 513 commercial 'brands' spread across a vast range of URLs.

In our experience the small volume of online CSA material paid for by conventional methods is due to how easily available free content can be and due to the fact that payment methods can act as identifiers.

In the world of child exploitation, different economics are at work. Abusive content itself can be a form of currency, valued based on how new it may be or its extremity. Criminals exchange images like-for-like, and the provision of new content can serve as a step up into exclusive rings that share select abuse content or even meet to commit abuse crimes in person.

Instead, criminals turn to hidden/anonymous services like TOR, P2P networks and even older tech like internet relay chat, as well as online payment systems and crypto currencies like BitCoin to allow identities to remain unknown. This makes it increasingly difficult for law enforcement to identify perpetrators and networks behind the production and distribution of child sexual abuse material. Without payment to provide the trail to abusers and distributors, police need to be able to track other markers, other currencies, such as the images and videos themselves.

Each image has a signature, as clear an identifier as bank details, and it's this that can be used to track and trace images, finding them on servers, storage services, devices, CDs and USB keys. Tracking the abuse-content itself, rather than the thousands of URLs where it is hosted, is vital if we are to find and stop the estimated 90 per cent of CSA material that is distributed 'for free'. The adage of 'following the money' remains true, but its important to remember that currency isn't always measured in notes and coins.