Australia's census website crashed and no-one is sure whether it was hackers or just incompetence

Australia is having a census nightmare.

First, here's what we know: The website for completing the census digitally went offline for several hours on Tuesday after technical issues.

But we don't know what actually happened.

$4 - which is believed to have stopped millions from completing the census - on the work of hackers, specifically a DDoS.

DDoS stands for Distributed Denial of Service attack, and it is where an attacker (or attackers) floods the target with malicious traffic from numerous sources - ultimately overwhelming it and crashing it.

"What you saw was the denial of service attack or a denial of service attempt which, as you know, is designed to prevent access to a website as opposed to getting into the server behind it. Some of those defences failed, frankly," Turnbull said - but he claims no Australians' data has been accessed or stolen by the alleged attackers.

Meanwhile, the Australian Bureau of Statistics' Chief Statistician $4 "overseas."

But not everyone is convinced by this explanation.

A digital attack map that maps DDoS activity around the world does not show unusual activity in Australia during the purported attacks - suggesting that more prosaic technical reasons may be behind the failure. $4 that "if this was a DDoS and not just rubbish capacity planning for a rendezvous condition [everyone doing the same thing at once on a website], I'll eat my hat."

The alternate theory, then, is that it wasn't attacked - but that the infrastructure put in place was simply inadequate for the incoming traffic. Or perhaps some combination of the two - a non-exceptional DDoS attack was exacerbated by poor technical planning. ($4 "confluence of events.")

Whatever the ultimate explanation for the outage, it's an embarrassing episode for the Australian government - $4.