Denmark's Nets has warned local banks and international card schemes of a data breach which may have compromised up to 100,000 credit cards.

The Danish payment processor has alerted banking customers to the hack, which it believes was linked to a single overseas Internet retailer.

It has called on local banks to replace the stolen cards. "By replacing possibly compromised cards preemptively, banks and shops can save an amount in the triple digit million (Danish crowns) range, which they could suffer in losses from trades made with stolen credit card information," the company says in a statement..

Reuters reports that Jyske Bank has already moved to block and replace 7000 cards caught up in the attack.

The company is working with Visa and MasterCard to investigate the breach.