Credit Suisse has called in outside experts to help find the source of a leak that exposed the details of accounts held by wealthy clients allegedely involved in torture, drug trafficking, money laundering, and corruption.

The huge trove of banking data was leaked by an anonymous whistleblower to the German newspaper Süddeutsche Zeitung. “I believe that Swiss banking secrecy laws are immoral,” the whistleblower source said in a statement. “The pretext of protecting financial privacy is merely a fig leaf covering the shameful role of Swiss banks as collaborators of tax evaders.”

Details of accounts linked to 30,000 Credit Suisse clients all over the world are contained in the leak, which unmasks the beneficiaries of more than 100bn Swiss francs.

A newspaper consortium examing the files has accused the bank of widespread failures of due diligence and repeated failures to weed out dubiuos clients and sources of illicit funds.

The Swiss bank says it "strongly rejects the allegations and insinuations about the bank’s purported business practices", pointing out that approximately 90% of the reviewed accounts are today closed or were in the process of closure prior to receipt of the press inquiries, of which over 60% were closed before 2015.

"These media allegations appear to be a concerted effort to discredit not only the bank but the Swiss financial market¬place as a whole, which has undergone significant changes over the last several years," states the bank. "In line with financial market reforms across the sector and in Switzerland, Credit Suisse has taken a series of significant additional measures over the last decade, including considerable further investments in combating financial crime."

Of the whistleblower leak, the bank states: "We take this latter allegation very seriously and will continue with our investigations with an internal task force including specialist external experts. We have robust data protection and data leakage prevention controls in place to protect our clients."