Silicon reports that Fraudsters stole the credit card details of 2,000 MasterCard holders in a major security breach last week.
Silicon was contacted by one customer of the Clydesdale Bank who was told that her MasterCard details, along with those of 2,000 other people, were "in the hands of a fraudster".
The Clydesdale Bank would not comment except to say it was advised of the problem by MasterCard.
MasterCard said it took immediate action together with all the banks concerned as soon as the breach was discovered.
A statement issued by MasterCard said: "In order to protect cardholders, MasterCard and its card-issuing banks operate state-of-the-art, multi-level fraud monitoring systems. Together, we look for patterns of activity consistent with fraud. Issuers can then monitor their cardholders' accounts closely for fraudulent activity and may reissue cards or take other actions if they suspect fraud has occurred."