The popular cryptocurrency Bitcoin has gained notoriety in sex trafficking cases after disabled credit card payments.

There are about 4.5 million people who have been forced into sexual exploitation. In the US, many of them end up advertised on Backpage, the second biggest classified ad listing site. People list everything from events to furniture there, but it has also become associated with sex ads and sex trafficking – so much so that the US National Center for Missing and Exploited Children has said that the majority of child sex trafficking cases referred to them involve ads on Backpage.

“The internet has facilitated a lot of methods that traffickers can take advantage of. They can easily reach big audiences and generate a lot of content without having to reveal themselves,” says Rebecca Portnoff at the University of California, Berkeley.

But a new tool developed by Portnoff and her colleagues can ferret traffickers out. It uses machine learning to spot common patterns in suspicious ads, and then uses publicly available information from the payment method used to pay for them – bitcoin – to help identify who placed them.

To identify the authors of online sex ads, Portnoff’s tool looks at the style in which ads are written. Artificial intelligence trained on thousands of different adverts highlights when similar styles have been used, and clusters together likely candidates for further investigation.

The second step comes via the payment method. Credit card companies stopped the use of their services on Backpage in 2015, leaving bitcoin as the only way to paying for adverts.

During a four-week period, the research team tried out their tool on 10,000 adverts. It correctly identified about 90 per cent of adverts that had the same author, with a false positive rate of only 1 per cent. One of the bitcoin wallets they tracked down was responsible for $150,000 worth of sex adverts, possible evidence of an exploitation ring.

The team is working with a number of different police forces and NGOs with the hope of using the tool in real investigations soon. The work was presented at the Conference on Knowledge Discovery and Data Mining in Canada this month.

Read more at New Scientist: AI uses bitcoin trail to find and help sex-trafficking victims

New Scientist

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