A hacker has threatened to reveal personal customer details of a Swiss bank unless it paid €10,000.
The Banque Cantonale de Genève (BCGE) said an attempted cyber attack, along with "further attempted coercion”, was thwarted.
Since the hacker threatened to reveal the personal details of 30,000 customers, the bank said it has put in place “additional protective and information measures” for any clients potentially affected.
BCGE said the information was stolen and published: “In line with an expected pattern of events, the bank duly observed that certain information has indeed been intercepted and published.”
The bank is now working with police and security experts to find out exactly what material has been released.
BCGE told customers to take extra care and attention when using the internet to bank.
More on cyber threats
The bank also warned of the possibility of inappropriate messages or calls being addressed to the clients concerned. "The BCGE recommends that no response be made to such communications,” it said.
Banks are regularly attacked by cyber criminals but much of it goes unreported. One source said there are constantly attempted attacks but most are unsuccessful.
A University of Cambridge researcher told a treasury select committee banks are under-reporting cyber fraud because they don’t want to scare customers.
Speaking at a meeting in November 2014 about the treatment of customers by finance firms, University of Cambridge senior researcher in security economics Dr Richard Clayton said: “Insiders tell me the going rate is about twice the amount of money [reported by banks] that goes walkies out of people’s accounts.”
One senior security professional in the banking sector said he thinks it is true banks carefully choose how they report cyber crime.
"The financial service industry relies on confidence in the system so anything that worries customers can hurt,” he said.