Referring to the Ablon et al$.$ report on markets for cybercrime tools and stolen data, what is the data source used by the authors for this study of hacker markets?

More than $2$ dozen interviews with subject$-$matter experts

An Analysis of the FBI's Internet Complaint Center $($ICC$)$ data over $10$ years Over $500$ hours of covert participant observation on hacker markets on the dark web

Surveys of over $100$ Chief Information Security Officers $($CISOs$)$ at large private corporations