Prime Minister Malcolm Turnbull has ordered an inquiry into the collapse of the online Census on Tuesday night, claiming contractor IBM "failed" to repel a "completely predictable" attack on the survey.

The PM's cybersecurity advisor Alastair MacGibbon has been directed to inquire into whether IBM did enough to protect the Census before four DoS attacks throughout Tuesday prompted the Australian Bureau of Statistics to take the site offline.

Turnbull today said the "completely predictable" DoS attacks weren't repelled because of "failures in the system that has been put in place for ABS by IBM".

He warned there would be "serious consequences" following the review.

“Measures that ought to have been in place to prevent these denial-of-service attacks interfering with access to the website were not put in place. That was a failure that was compounded by some failures in hardware – technical hardware failures – and inadequate redundancy," Turnbull told 2GB radio this morning.

“The contract with IBM was announced in late 2014 – IBM has done this before, but there has clearly been a failure in the work that was done."

MacGibbon's inquiry will be the second into the Census catastrophe alongside the Privacy Commissioner's investigaiton into whether any customer data was compromised.

Timothy Pilgrim yesterday promised to formally investigate the IT bungle less than 24 hours after stating he was “generally satisfied” with the security provisions put in place to protect the sensitive data.

“My first priority is to ensure that no personal information has been compromised as a result,” Pilgrim said in a statement.

Small business minister Michael McCormack yesterday insisted that no data was compromised.

The ABS expects to recommission the online Census today. It has been working with the Australian Signals Directorate to identify the source of the attack.

The issues were attributed to the four DoS attempts throughout Tuesday combined with the subsequent failure of the Census' geoblocking function (which was switched on to combat the overseas DoS) and the collapse of a router.