FBI agent Kyle Armstrong said the Bureau has 130 ongoing crypto-related cases, with dark web drug sales a particular concern, Bloomberg reported Wednesday, June 27.

Speaking at the Crypto Evolved conference in New York on Wednesday, the supervisory special agent said the number represented “a small sliver,” of the FBI’s activities, which number “thousands of cases.” The agency has nonetheless noticed an increase in illegal activity facilitated by cryptocurrency payments, he said.

The 130 “threat tagged” files related to crypto span a gamut of crimes, including human trafficking, kidnapping, ransomware attacks and illicit drug sales.

This latter has become a focus for the Bureau, according to Armstrong, highlighting the opioid epidemic in the U.S. He considered the dark web to be a factor in enabling drug abuse, saying that 10 percent of global drug users make their purchases on illegal online marketplaces.

Armstrong’s figure of 10 percent is notably not higher than statistics released by an older Global Drug Survey from 2017, which found the global median for the percentage of drug users who use the darknet to be 10.1 percent. 90 percent then, continue to purchase illicit substances via more ‘traditional’ methods.

Armstrong, who manages the three-year-old Virtual Currency Initiative for the FBI as it relates to money laundering activities, said that while the underlying blockchain technology makes it easier for investigators to trace cryptocurrencies than cash, the relative anonymity of transactions can prove an obstacle.

In February, a two-year study of the dark web ecosystem claimed that Bitcoin may in fact be losing its cachet as the most popular currency on dark web markets, seemingly due to consumers’ annoyance at network traffic and high transaction fees.