A cyberattack on Arnold’s supermarket has led to customers’ cards being used in fraudulent transactions, it was revealed last night.

The shock news came after Arnold’s store chain chief Frank Arnold said the banker HSBC had alerted the firm to a raid on its computer servers.

“This has resulted in overseas fraudsters accessing information from some of the cards used for transactions at our stores and making purchases abroad over the course of the last five weeks,” Mr Arnold said.

He was unable to say how many cards had been put at risk, but thousands of shoppers will have used the store chain in the busy run-up to Christmas and the new year. Mr Arnold said that HSBC had notified the chain of the attack last Friday and that stores had immediately stopped accepting cards.

He added that a team of IT specialists had been brought in to try to plug the breach.

“They have worked tirelessly over the weekend and we are making sure that our systems are once again secure,” he said.

He added that it was hoped that the firm would be able to accept cards by the end of today — using a new wireless system provided by HSBC.

Mr Arnold said that customers should check their bank statements for suspicious transactions dating back to the start of last month.

“In the event that customers suspect any irregular activity on their card, I would request them to contact their bank directly,” he added.

“I sincerely apologise for any inconvenience that this attack may have caused.”

Mr Arnold pledged that the firm would continue to work to fix the problem and that he would issue regular updates.

A spokeswoman for HSBC said its cards, along with those issued by other Island banks, were among those affected by the hacking attack. The bank did not respond to questions about how many cards had been affected and where the attack had come from.

She added: “The matter is under investigation.

“We have taken preliminary precautionary measures, however, in the event a customer suspects any irregular activity on their cards, we request them to immediately inform the bank.”