In 2012 (the most recent statistics available), Backpage hosted about 70% of all online advertisements for sexual services in the United States. Unfortunately, many of these ads list sexual services from children; in fact, the United States National Center for Missing and Exploited children has reported that more than half of the cases that they handle have something to do with ads placed on Backpage.
Although many of these BackPage advertisements manage to fly under the radar, there can be some common patterns between them that can be used to identify suspicious activity. A single sex trafficker is likely to post a number of advertisements from the same computer and with the same writing style. Therefore, identifying groups of advertisements that have the same writing style can lead to the discovery of rings of exploitation. 
However, these patterns are not always easy for human investigators to spot–there are hundreds of thousands of ads on BackPage. Additionally, the advertisements each list a different victim of trafficking, rather than the traffickers themselves.
AI Identifies Writing Style, Common Threads Between Advertisements
That’s where AI comes in. Rebecca Portnoff, a PhD candidate at the University of California Berkeley, has worked together with a team of researchers to create an AI that analyzes things like writing style, timestamps, and the prices of advertisements on Backpage and sites like it to identify groups of ads authored by a single person.
When a particular style has been consistently identified, the associated ads are clustered together into a group for further investigation.
Once a suspicious group of advertisements has been identified, Portnoff’s AI commences scouring and analysis of Bitcoin’s public ledger (its blockchain) to identify which Bitcoin wallet addresses are associated with which ad.
Since credit cards cannot be used on BackPage, Bitcoin is the only way to pay for advertisements. If a group of advertisements with a shared writing style also share a Bitcoin address, the AI saves that information as well.
Once the Bitcoin address has been identified, law enforcement officers use it in combination with the rest of the information gathered by the AI to proceed with an official investigation. In its trial use, Portnoff’s AI tool analyzed 10,000 ads and managed to recognize 90% of posts that were authored by the same person. In the same trial, the AI identified a suspicious Bitcoin address associated with $150,000 in advertisements.
How Anonymous is Bitcoin?
Frankly, Bitcoin is not the cryptocurrency best suited for nefarious purposes. In fact, it is odd that criminals continue to use it as such. Bitcoin is indeed “pseudonymous”, but it is not as anonymous as coins like Zcash or Monero, which were both developed to be more anonymous than Bitcoin.
While Bitcoin was originally developed to be a form of “digital cash” that was as anonymous as paying for something in fiat, other technologies have been developed to reveal Bitcoin users’ offline identities.
All of the transactions that involve Bitcoin as a means of payment are permanently stored on Bitcoin’s blockchain. While the actual identities of Bitcoin users are obscured, each user does have a wallet address that can be used to track transactions.
When a transactional pattern is identified, this information can be used in conjunction with other pieces of information to discover the identity of the user.
Bitcoin’s Storied Past: Long Association with Criminal Use
Although Bitcoin has made significant strides toward being a more “legitimate” and widely recognized form of payment, many BTC-skeptics persistently associate its use with criminal activity. Their feelings are not unfounded–Bitcoin was the main form of payment used on the infamous, now-defunct Silk Road network.
Silk Road was mainly a platform for buying and selling drugs and other contraband materials, but more sinister products and services could also be bought and sold on the network. Assassinations and illegal weapons could be found there for purchase; Silk Road was also used to exploit victims of sex trafficking.
While Bitcoin’s lack of complete anonymity may be a deterrence for non-criminal users who simply value their privacy, it is a blessing to the women, children, and men who are victimized by sex traffickers.