Raids have been staged across Germany against hundreds of suspected tax evaders. Prosecutors in Bochum city who coordinated Monday's action say the tips came from a CD listing German clients of the Swiss bank UBS.
Fifty tax inspectors and numerous prosecutors had visited the homes and business of "several hundred" suspects in many of Germany's 16 regional states, said Bernd Bieniossek, a leading prosecutor in the western German city.
Reacting on Monday, the Zurich-based UBS said 2009 had been a watershed and since then it had avoided aiding cross-border tax evaders. In August, UBS's new chief Axel Weber said his bank had "zero tolerance" for tax fraud.
Germany's mass tabloid newspaper "Bild" broke the raids story on Monday, saying the latest data CD was one of six purchased since 2010 by the Düsseldorf-based finance ministry of North Rhine-Westphalia (NRW) state. Detectives had obtained the CD three months ago, Bild said.
Bieniossek said that CD also contained details of trust accounts that suspects might have used in Switzerland to evade tax payments in Germany.
Tax treaty wrangle unresolved
NRW's Social Democrat (SPD)-led government, notably Finance Minister Norbert Walter-Borjans, has repeatedly defended such CD purchases despite criticism from Chancellor Angela Merkel's center-right coalition government.
For months, Merkel's federal finance minister Wolfgang Schäuble has sought to finalize a tax treaty with Switzerland which would collect back-dated tax on Germany's behalf. But this move has been blocked in Germany's upper house of parliament by regional states governed by the SPD and the Greens.
UBS long under scrutiny
NRW's finance ministry said probes and self-imposed charges filed by suspected tax evaders since 2010 had generated more than three billion euros ($3.8 billion) in extra revenues. It said the six CDs had also listed clients of the banks Julius Bär and Credit Suisse.
Last Friday, Mannheim prosecutors said that since March they had investigated claims that UBS customers' funds might have been moved through an internal account from Germany to Switzerland.
UBS replied that its own internal investigations had "not revealed any indication of misconduct on the part of UBS Deutschland AB."
Authorities raided the UBS's Frankfurt premises in May and seized electronic records, which are still being evaluated
Switzerland's long tradition of banking secrecy has come under increasing pressure within Europe and the United States. A 2008 US tax probe resulted in heavy fines.