Australia's Privacy Commissioner is to investigate Vodafone for compromising the security of four million customers' personal details.
The mobile phone giant on Sunday admitted its online database was breached, allowing customer information to be accessed.
It is understood the security compromise only affects Vodafone customers in Australia.
Vodafone had to reset log-ins for thousands of dealers and employees after it emerged the personal details of customers were accessible from any computer.
Home addresses, driver's licence numbers and credit card details were made available, as well as information on who the customer calls or texts.
Australian media is reporting criminal groups have been paying to get the information, as have spouses keeping tabs on their partners' communications.
Privacy Commissioner Timothy Pilgrim says he is concerned about the amount of personal information that may have been disclosed, some of which could be sensitive.
Mr Pilgrim will first try to establish if Vodafone has breached the Privacy Act.
NZ customers safe - Vodafone
Vodafone in New Zealand is asssuring its customers their private information is safe and can only be accessed by approved personnel through a procedure that requires more than a username and password.
The company says access to customer accounts is monitored and any unusual activity is investigated.
Technology consultant Colin Jackson says the security breach in Australia should prompt businesses in New Zealand with similar systems to put greater checks in place.
As details of who customers call and text are available, Vodafone users could be targeted by organised crime and identity theft, as well as stalking, he warns.