Property valuation firm LandMark White is under fire over a major data breach, in which home loan details of 100,000 customers were hacked, according to a report by The Sydney Morning Herald.

The breach, which was confirmed on Friday, could include property valuations and personal contact information (first and last names, residential addresses, and contact numbers) of homeowners, residents, and property agents.

LandMark White is one of the valuation firms used by banks and other lenders across the nation to evaluate mortgage applications.

Commonwealth Bank of Australia and ANZ Bank announced on Tuesday that they had suspended LandMark. National Australia Bank did the same and was still gauging the impact on its customers, while Westpac did not comment on the issue.

"As part of the data incident, customer information relating to property valuations was found hidden on the internet. The customer information that was disclosed relates directly to the valuations completed by LandMark White and includes customer name; contact details such as phone or email address; and details about the valued property,” Commonwealth Bank said in a statement.

A source told The Sydney Morning Herald that the bank was contacting more than 20,000 customers in the wake of the breach. The bank also assured consumers that no bank account information was disclosed in the breach.

ANZ was also assessing how its customers were affected. ''We will contact them directly to outline potential impacts and how we will support them. At this stage we understand a very small percentage of our customers who had valuations undertaken between November 2015 and December 2018 are potentially impacted,'' ANZ Chief Data Officer Emma Gray said.

ANZ had suspended the use of LandMark White and believed that no other valuers were involved in the breach.

"ANZ takes its privacy obligations very seriously and we are extremely disappointed this incident has occurred," Gray said.

LandMark White has launched a website to cater to its customers and said there was no evidence of misuse of any information although the incident is still “under close review.''

"We are working closely with experts in IT and cybersecurity, as well as our corporate partners, to achieve the best possible outcome for our clients. LandMark White acted immediately, employing independent experts in data breaches and cybersecurity to assist with the investigation into the incident," LandMark White Chief Executive Chris Coonan said.

The firm also claimed that they informed the authorities as soon as they knew about the issue. ''Although LandMark White's investigation is ongoing, we have taken immediate steps to prevent any further disclosure of data. Currently, there is no evidence of misuse of any information. We will share new information as soon as possible,” Coonan said.