Swiss tax returns available on the darknet

On 8 November 2021, the Swiss newspaper Le Temps revealed that an investigator exploring the darknet had discovered tax documents of Swiss individuals and companies for the year 2020.

This sensitive data includes, for some clients, their name, address, and social insurance number (AVS), amounts owed to the municipality, canton and Confederation, and payment slips containing precise information on bank accounts and outstanding mortgages.

These tax documents belong to citizens and companies based in the cantons of Zurich, Zug, and Schwyz. According to Le Temps, this leak is the result of the hacking of a fiduciary in the canton of Schwyz that has offices in the canton of Zurich. In Switzerland, a fiduciary is a firm that provides administrative services to natural and artificial persons. Its duties may include managing bank accounts, accounting, and tax returns.

The darknet specialist hypothesises that this fiduciary must have been the victim of ransomware: its files were encrypted and stolen and, as it refused to pay the ransom, the hackers put all or part of these files online on the darknet.