Prime Minister Malcolm Turnbull is vowing that "heads will roll" after this week's denial of service (DoS) attacks against the Australian Bureau of Statistics (ABS) which effectively brought the census to a halt.

"Which heads roll, where and when, will be determined once the review is complete," Mr. Turbull said to reporters in Canberra.  "I made it very, very clear that what we needed to do was be absolutely straight and frank with the Australian people.

"This has been a failure of the ABS," he declared.

Turnbull says his cyber security adviser Alastair MacGibbon will conduct a review of what happened, to be assisted by the Australian Signals Directorate.  Meanwhile, Senator Nick Xenophon is preparing a separate inquiry in the Senate.  "This is an international embarrassment. But it's more than embarrassing, it points to a very serious failure of a very important government program," Senator Xenophon told ABC Radio National.  He says Australian taxpayers ought to get a refund of their investment from IBM and other contractors chosen by the ABS to put together the census system.

But the PM disagrees with the notion that contractors are responsible:  "The denial of service attacks were completely predictable [and] should have been repelled readily. They weren't because of failures in the system that had been put in place for ABS by IBM," Mr. Turnbull said to 2GB Radio.  "There is no doubt there were failures in the system's preparation for an entirely predictable denial of service attack.  Measures that ought to have been in place to prevent these denial of service attacks were not put in place."

A denial of service attack is a malicious attack on a server designed to render it useless to the people it was meant to serve.  They're often disguised as legitimate internet traffic that quickly escalates into a flood of digital information that overwhelms the target.  DoS attacks on the ABS server began on the morning of 9 August; by that evening, safeguards failed that would have blocked overseas traffic accessing the ABS system.  Officials decided to take it offline, a decision criticized by PM Turnbull.