I would imagine that OPs could be thinking of the recent story (https://www.bbc.co.uk/news/business-59990477 https://www.bbc.co.uk/news/business-59990477) about

I would imagine that OPs could be thinking of the recent story (https://www.bbc.co.uk/news/business-59990477 https://www.bbc.co.uk/news/business-59990477) about North Korean stealing $400m of crypto. It seems reasonable to suggest that groups who want to avoid scrutiny by various authorities would make use of a system which isn't covered well by standard regulators who are under the control of those authorities. Additionally there are a number of crypto currencies who provide anonymous transactions (e.g. Monero) which is obviously going to attract people who want to move money covertly. Terrorists would be one example of such groups of people.