German prosecutors have raided 13 branches of the Swiss bank Credit Suisse in connection with an inquiry into tax fraud.
The prosecutor's office in Dusseldorf said on Wednesday that about 150 investigators took part in searches.
The search is focusing on allegations that bank staff assisted clients to evade taxes.
Tax officials bought a CD in February that reportedly contained information on about 1,100 wealthy Germans.
There were reports at the time that the authorities paid about 2.5m euros for the disc to an unnamed individual.
The data contained information that led prosecutors to believe that some 1.2bn euros (£1bn) of undeclared income was stashed in the Swiss accounts by the 1,100 people.
Investigations were launched into the individuals, but now officials have turned their attention to bank staff for allegedly aiding and abetting customers to avoid taxes.
In April, Credit Suisse's chief executive Renato Fassbind said it appeared increasingly likely that some of the bank's clients were listed on a disc containing stolen data.
The company was not immediately available for comment on Wednesday's raids.
Governments in Europe and the US have been cracking down on tax evasion.
It is not the first time that Germany is thought to have paid for data on bank customers.
In France and the UK too, authorities have bought information on wealthy bank customers who may have hidden money in secret accounts.