In a cyberattack on an Irish marketing company, Loyaltybuild, the hackers have reportedly stolen full card details of at least 376,000 people.
Loyaltybuild runs reward schemes for companies across Europe, including one for the Irish supermarket chain SuperValu.
According to Sky News, the hack-attack affected more than a million people, whose phone numbers and addresses were also stolen, while some 70,000 SuperValu customers had their full card details compromised.
The Office of the Data Protection Commissioner (ODPC) confirmed the extent of the breach and said that the details of an additional 150,000 clients were also stolen.
Loyaltybuild said that it had been the victim of a sophisticated criminal attack and that it was urgently investigating what had happened.
Meanwhile, Ireland's data commissioner Billy Hawkes said that the ODPC has warned customers to be vigilant in relation to their accounts and to report any suspicious transactions to their card company, adding that the Interpol may have to be called in, the report added.
