Hackers have stolen data on more than 600,000 Domino's Pizza customers in Belgium and France, the company said, and an anonymous Twitter user threatened to publish the data unless Domino's pays a cash ransom.

Customer names, delivery addresses, phone numbers, email addresses and passwords were taken from a server used in an online ordering system that the company is in the process of replacing, Domino's spokesman Chris Brandon said on Monday.

He said he did not know if the stolen passwords had been encrypted.

A Tweet directed at Domino's customers through an account of somebody listed as "Rex Mundi" said hackers would publish the customer data on the Internet unless the company pays 30,000 euros ($40,800), according to an article in The Telegraph.

The Rex Mundi account was later suspended.

The group also posted a message to the pastebin site dpaste.de boasting about the hack,

Domino's has some 11,000 stores worldwide, including 229 in France, 24 in Belgium and about 5,000 in the United States.

News of the hack came on the same day that Domino's announced an app in the U.S. that lets people order pizzas with the help of a voice-activated digital assistant named Dom.

(NBC)