Prosecutors said they were investigating HSBC Private Bank (Suisse) SA and persons unknown for suspected aggravated money laundering. The investigation could later be extended to people suspected of committing or participating in money laundering, they said in a statement.
The investigation stemmed from "the recent public revelations" about the private bank, prosecutors said. They said a search at its premises in Geneva was carried out Wednesday, but gave no details.
Last week's report from the International Consortium of Investigative Journalists and several news organizations found that the bank hid millions of dollars as it helped wealthy people around the world dodge taxes.
It was based on leaked documents covering the period up to 2007 and relating to accounts worth $100 billion held by more than 100,000 people and legal entities from 200 countries.
A former HSBC employee, Herve Falciani, gave the data to French tax authorities in 2008. France shared it with other governments and launched investigations. The French newspaper Le Monde obtained a version of the data and shared the material with the ICJ, which analyzed the material together with other international media.
Some details of such operations were disclosed previously, when HSBC — which is based in London but has operations globally — was fined in 2012 by the U.S. for allowing criminals to use its branches for money laundering. But this month's report disclosed a more detailed cache of data and information.
"We have co-operated continuously with the Swiss authorities since first becoming aware of the data theft in 2008 and we continue to co-operate," HSBC's Swiss subsidiary said in a brief emailed statement Wednesday.
Its CEO, Franco Morra, said last week that the private bank had shut down accounts from clients who "did not meet our high standards," and that the revelations about "historical business practices" were a reminder that the old business model of Swiss private banking was no longer acceptable.
Prosecutors said they were targeting the HSBC private bank under a law that allows companies to be investigated independently of whether any employees are culpable "if it can be accused of not having taken all the organizational measures necessary" to prevent violations of the law.
Last year, Swiss authorities indicted Falciani on charges of data theft and said they may try him in absentia.
Frank Jordans contributed to this report.