Defence officials grilled over entering new PwC contracts after confidentiality scandal revealed

Department of Defence officials stuck to their speaking points on Tuesday when answering questions regarding their dealings with the big four firm at a Senate estimates hearing.

But questioning by Greens senator David Shoebridge revealed at least two new contracts had been entered into with PwC this month.

The scandal first surfaced in January after then-international tax head, Peter Collins, was revealed to have allegedly shared privileged multinational tax avoidance information from the tax office to others in the firm.

The incident was referred to the Australian Federal Police for investigation by the Treasury Department in May.

Associate secretary Matt Yannopoulos said he didn't know why more PwC contracts had been signed off in recent weeks, taking on notice further details regarding a contract for audit services, valued at $142,000, and another for asset accounting services in the Joint Strike Fighter branch, worth $139,000.

Mr Yannopoulos said the department held 54 contracts in total with the provider, valued up to $223.3 million.

Department secretary Greg Moriarty said his staff were working in a "methodical way" to determine how it will deal with PwC's existing and historical contracts.

He added his department was following whole-of-government guidance and advice, despite being personally "very struck by the extent of the wrongdoing" by PwC.

Labor senator Jenny McAllister, who represented the Defence Minister, reminded senators "there isn't a general prohibition on contracting with PwC".

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The Finance Department issued a stern warning last week in the wake of the firm's actions being referred to federal police.

Adjustments to government contracts will allow public officials to terminate contracts if an adverse event, including an event which is outside a specific contract, occurs.

"These actions deliver a clear message to suppliers that unethical behaviour will not be tolerated, whether it occurs as part of a procurement arrangement or as part of another arrangement with government," department secretary Jenny Wilkinson told a Senate estimates hearing.

Senator Shoebridge earlier asked the department's top brass whether it was confident those involved in the tax advice confidentiality breach earlier this year were not also involved in one of its 54 contracts.

Mr Yannopoulos said he had received assurances from PwC last week, and again on Monday, they were not.

A series of redacted emails from the firm naming at least 54 individuals were tabled in the Senate earlier in May.

Mr Moriarty said neither he, nor his department, had received the unredacted list of PwC employees to crosscheck with those involved in Defence contracts.

The Greens senator asked why Mr Moriarty relied on the firm's assurances rather than having his staff independently verify it.

"When we get formal correspondence from very senior people in PwC, who are trying to deal with this issue," Mr Moriarty said.

"I accept that there have been some very significant and very appalling breaches of public trust and the law, probably, but we are working through this methodically."

Senator Shoebridge responded, asking whether it was because the secretary didn't want to "upset" the firm.

"No," Mr Moriarty said in response.

Earlier, the department's chief information officer Justin Keefe admitted he had not undertaken additional integrity checks since early May.

One IT project with PwC for its secret internal network totalled $19.2 million.

The network allowed Defence officials to communicate with other agencies, such as the Department of Foreign Affairs and Trade.

"I have not undertaken any further assurances beyond the normal ones that we would undertake prior to anyone having access to our secret networks," Mr Keefe said.

The secretary would not be drawn on the Greens senators questions, adding his officials were working on their response in a "methodical" way.

"Not methodical, glacial," Senator Shoebridge said.

"That's your words, senator," Mr Moriarty said in response.