More than 1.1 million customers and clients of a marketing firm have been the victim of hackers.

Cyber crime experts investigating an attack on Loyaltybuild, which runs rewards schemes for companies across Europe, found more than 376,000 people have had their credit card details stolen. The details of an additional 150,000 clients were potentially compromised in an attack on its data centre in Ireland.

Ireland’s Data Protection Commissioner Billy Hawkes also revealed that the name, address, phone number and email address of 1.12 million clients were taken. “The initial indications are that these breaches were an external criminal act,” the watchdog said after being called in earlier today.

Loyaltybuild said it had been the victim of a sophisticated criminal attack.

It first raised concerns about a data security breach last month and the problem was initially thought to be limited to customers in Ireland. More than 70,000 customers of the supermarket SuperValu and over 8,000 at the insurance firm Axa were hit. Stena Line customers in Ireland may also be affected.