Australia has been warned its airports are vulnerable to infiltration by terrorists.
A leading international security specialist is urging authorities to be more alert for cyber hacking and attacks at the country's key transport hubs.
The fatal attack on a Brussels airport eight months ago, killing 31 people, prompted already nervous airport managers around the world to re-examine their own security systems.
Now, the Federal Government has received warnings from a United Nations security adviser that Australian airports could be susceptible to catastrophic attacks.
While security is generally tight, Dr Jim Kent says terrorist groups could still work their way into an airport "like a virus."
United Nations security advisor Dr Jim Kent. Source: YouTube
He cites, for example, covert infiltration of baggage handlers, immigration staff, freight drivers and pilot and cabin crews."
Dr Kent says he fears too little is being done to link suspicious activities with security measures.
Deakin University terrorism analyst Greg Barton, while more reassuring about any threat, says he agrees there is concern about authorities keeping up with technological advances.
Greg Barton Source: SBS Feed
"Airports, in terms of security around terrorism, (it's) pretty good -- for the big airports. Not so good for regional airports, where we haven't had the threat, frankly, but that's something that has to be thought about. Cyber hacking, we really don't know. It's a never-ending sort of cat-and-mouse game,* as far as technology and intent goes, that we have to always be looking at."
Just last week, Australian Federal Police revealed air-traffic-control messages at Melbourne had been hacked, but not by a person with serious intent.
Recent cases of corruption and illegal imports at airports have also left open the prospect of potential terrorists exploiting the same breaches. 
But Prime Minister Malcolm Turnbull insists Australia's police and intelligence services are the best in the world.
Australian Prime Minister Malcolm Turnbull Source: AAP
"We are very keenly alert to the threat of terror. But it is an abiding responsibility of government and of the courageous and really professional men and women in our security, police, intelligence services that keep us safe."
Australian security analysts say it is not just airports facing the challenge of keeping up with the latest counter-terrorism techniques.
With thousands of passengers passing through every day, Greg Barton says other key transport hubs are also very aware of their own vulnerabilities.
"Airports, like train stations, like bus stations and other sorts of transport hubs, they're not just for transport. You have cafes, you have shops -- in some cases, quite elaborate shopping centres set up, very large car parks. You've got to have a free flow of people through the door. You can't be scanning people right at the perimeter."
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