Mass circulation Bild reported that the government in the state of North Rhine-Westphalia had bought a disc for a "seven figure sum" in cash concerning clients suspected of parking assets away from the German taxman in Switzerland.
This followed reports last week of the purchase of a disc containing data on around 1,000 German clients of the private bank Coutts, this time for €3.5 million ($4.3 million).
According to German media, between €130 billion and €180 billion in German assets are hidden in Switzerland.
A tax deal between the two countries, aimed at ending such disputes, is to take effect in January 2013 but still needs to be ratified by both parliaments.
The federal finance ministry reacted with dismay to the first purchase, with spokesman Martin Kotthaus saying it "would have been fairer and more simple to have a standardized procedure" for dealing with tax evasion.
"This is what the tax accord signed with Switzerland will do," he added.
The two neighbours became embroiled in a major row in 2010 when German authorities raided branches of Credit Suisse bank in 13 German cities after buying data on suspected tax dodgers.
Switzerland reacted angrily, saying the data — bought for a reported €2.5 million — was stolen in violation of its banking secrecy laws.