British bank HSBC says information on 15,000 customers with accounts in Switzerland has been stolen.
HSBC says a former employee stole the information in late 2006 and early 2007. The accounts were all opened before October 2006.
The bank says it has contacted the affected customers and apologized for the breach of their privacy.
It said Thursday the stolen information only affects accounts in Switzerland with the exception of its former subsidiary HSBC Guyerzeller Bank.
Several banks in Liechtenstein and Switzerland have become victims of data theft in recent years.
The information has in some cases been offered to foreign governments seeking to track down nationals who have avoided paying their taxes by hiding money in Swiss accounts.