Dixons Carphone (LON:DC) shares plummeted over 4 percent at market open on Wednesday, after admitting to a huge data breach affecting 1.2 million people.

Hackers “attempted to compromise” 5.9 million payment cards, but Dixons Carphone said only 105,000 cards without chip-and-pin protection had been leaked.

The group added that there was no evidence that any of the cards had been used fraudulently following the breach, but chief executive Alex Baldock said it was “extremely disappointed” by the data breach and “sorry for any upset”.

“The protection of our data has to be at the heart of our business, and we’ve fallen short here.

“We’ve taken action to close off this unauthorised access and though we have currently no evidence of fraud as a result of these incidents, we are taking this extremely seriously,” he added.

The news comes as a further blow to Dixons Carphone investors, just a month after it warned that it had been affected by the tough market conditions and said it may suffer a sharp fall in profits.

Shares in the company are currently trading down 4.12 percent at 189.60 (0842GMT).