Federal police are hunting a gang of identity thieves who have been hacking the tax file numbers of up to 500 Australians a day.

The sophisticated online fraudsters have breached payroll systems, harvesting extensive personal details of workers and using the information to lodge fraudulent tax returns.

The revelation is the latest evidence of a large-scale identity fraud problem against government sites and services such as like MyGov, Medicare and the ATO and Labor wants a national investigation. 

In one case this month, payroll software used by a Melbourne accounting firm was hacked and the personal and financial details of 1600 employees of its clients were obtained.

An alarming level of personal data was plundered including, names, address, dates of birth, tax file numbers, bank account details, gross earnings and superannuation funds and membership numbers.

The scammers then prepared and lodged tax returns in the names of some of the unwitting workers.

It is was also confirmed  to victims that MyGov accounts could have been accessed and changed, or new accounts created using the stolen data, potentially leading to all services linked to the federal government web portal, including Medicare, Centrelink and Child Support, being compromised as well.