Rhineland Palatinate paid out €4 million for the disc, which held data suggesting around 10,000 Germans had collectively saved €500 million in taxes by putting money in offshore banks, the state's Finance Minister Carsten Kühl confirmed.
The data was, he said, authentic and of first-rate quality. It showed that money was being kept in accounts at banks Credit Suisse and Neue Aargauer Bank.
Employees from both banks are under investigation for assisting tax evasion, the Koblenz state prosecutor said, and cases against 201 German clients are now being prepared.
The federal finance ministry is thought to be using the CD as a way to open up conversation with Switzerland about banking.
In a statement released on Tuesday, the ministry said it stood behind Rhineland Palatinate's decision to buy the CD, which Der Spiegel magazine said first surfaced last year.