In an investigative report, two reporters for Wirtschaftswoche met last month with two individuals, arranged through an intermediary, who offered to sell a CD-ROM containing the names, addresses, bank name and account numbers of 21 million people, the magazine said.
"We took away with us the first delivery, a CD with 1.2 million accounts, that we couldn't imagine," said the editors in charge of the investigation, which has caused an uproar in Germany.
The economic weekly has given authorities the file, which supposedly would allow someone to commit fraud on a large scale.
"In the worst case, three out of four German households would have to be afraid that some money could be taken from their checking account without their authorisation, and perhaps even without their realising it," the magazine wrote.
For Peter Schaar, the government official in charge of protecting personal data, the incident reported by the magazine shows the need for tougher legislation.
"It is essential that personal data cannot be transmitted with the individual's explicit agreement, and that the source of the data is clearly identified in order to assure that one can follow up," Schaar told on ZDF television.