A confidentiality breach by the federal government's $5 billion infrastructure body shows it is now considering loaning public money to two new rail lines supporting mining projects.

The unintended leak of classified documents by the vaunted Northern Australia Infrastructure Facility shows it has been approached for funding by the proponents of the Balla Balla project, which comprises a port and railway to the Pilbara Iron Ore project in Western Australia. The port, rail line and a new mine are expected to cost about $6 billion.

To protect the identity of the source, Fairfax Media cannot reveal exactly how it obtained information from the documents. However the method reveals critical shortcomings in the way NAIF handles and secures sensitive information.

The facility's confidentiality policy states that staff must "keep all confidential information properly secure … Any confidential information taken home for work purposes should be properly protected and secured at all times".