  The COVID-19 pandemic has reshaped the demand for goods and services
worldwide. The combination of a public health emergency, economic distress, and
misinformation-driven panic have pushed customers and vendors towards the
shadow economy. In particular, dark web marketplaces (DWMs), commercial
websites accessible via free software, have gained significant popularity.
Here, we analyse 851,199 listings extracted from 30 DWMs between January 1,
2020 and November 16, 2020. We identify 788 listings directly related to
COVID-19 products and monitor the temporal evolution of product categories
including Personal Protective Equipment (PPE), medicines (e.g.,
hydroxyclorochine), and medical frauds. Finally, we compare trends in their
temporal evolution with variations in public attention, as measured by Twitter
posts and Wikipedia page visits. We reveal how the online shadow economy has
evolved during the COVID-19 pandemic and highlight the importance of a
continuous monitoring of DWMs, especially now that real vaccines are available
and in short supply. We anticipate our analysis will be of interest both to
researchers and public agencies focused on the protection of public health.

Computers and Society;Social and Information Networks;Physics and Society