Giant US retailer, Target, says its recent data breach effected about 70 million customers, more than it initially estimated, and that the hacking incident had hit December sales.

Target, one of the biggest US retailers, sharply lowered its fourth-quarter earnings outlook and said it was unable yet to estimate the costs related to the breach.

Target revealed on December 19 its payment card data had been breached, affecting about 40 million customers.

The stolen data included credit and debit card data, customer names and PIN numbers.

But in investigating the November 27-December 15 breach, Target said, it uncovered other types of information were also stolen.

The information theft includes names, mailing addresses, phone numbers, or email addresses for up to 70 million people, it said in a statement.

“I know that it is frustrating for our guests to learn that this information was taken and we are truly sorry they are having to endure this,” Gregg Steinhafel, Target chairman, president and CEO, said.

Target said consumers would have “zero liability” due to any fraudulent charges arising from the breach. It offered one year of free credit monitoring protection.

Target also said fourth-quarter earnings had been hit by “meaningfully weaker than expected sales” since it disclosed the data breach.

Target now expects fourth-quarter comparable store sales to decline 2.5 per cent from its prior forecast of flat sales.

AFP