Hi there,
As a general rule, Swiss banks do not accept liability for fraudulent transactions when your bank information is stolen over the internet (when you use online banking or email banking, for example). The main reason for this is that the bank has no control over your devices, software, email servers and online habits. When bank details are stolen using malware or other harmful software on your computer, there is nothing the bank can do about it and no way that they can verify that transactions are in fact fraudulent.
However, banks tend to be accomodating with regards to online banking and may reimburse part of the loss if there is sufficient reason to believe that transaction made were indeed fraudulent.
If the theft results from a skimmed or stolen debit card, most Swiss banks will be more accomodating. In many cases banks will reimburse at least part of the stolen money. The moneyland.ch guide to protecting yourself from card skimming provides useful tips on protecting your card data.
Best regards from Moneyguru