Nearly 50,000 Australians and 5000 federal public servants have had sensitive personal information exposed online as part of one of the nation's biggest ever data breaches.

Employees of the Department of Finance, the Australian Electoral Commission and National Disability Insurance Agency have been caught up in the massive leak caused by a private contractor, along with more than 40,000 private sector workers from insurer AMP, utility UGL and Dutch multinational Rabobank.

The leaked information included names, passwords, ID data, phone numbers, as well as credit card numbers and corporate information including salaries and expenses, IT News reported on Thursday.

The Department of Prime Minister and Cabinet confirmed it was aware of a breach involving a third party contractor, but said the data exposed was historical, archived and partially anonymised.