Pizza Hut says hackers gained access to the personal information of its customers via its website.
Users of the Whirlpool broadband forum and social news website Reddit first noticed the pizza maker's website had been defaced on Tuesday night, and on Wednesday evening Pizza Hut general manager Graeme Houston issued a statement to technology websites ZDNet and Gizmodo confirming details had been stolen too.
While the site was defaced it included a link to rival pizza maker Dominos, according to a screen grab.
"Pizza Hut can confirm that a layer of its website, pizzahut.com.au, was breached with access gained to names and contact information, including email addresses," Mr Houston said in a statement to Gizmodo.
He didn't say how many customers were affected or who Pizza Hut believed was responsible.
"We are working with our website providers to conduct a thorough investigation of the matter and have also reported the incident to the Office of the Australian Information Commissioner," he said.
"We would like to reassure all of our customers that absolutely no credit card information was stolen and there is no need for concern regarding credit cards.
"The security of our online ordering system has not been compromised in any way and our customers can continue to order online in the knowledge the ordering system is secure."