As the siege continues — with as many as 50 hostages being held at gunpoint inside the Lindt Cafe in the CBD — it is becoming clear that December 15, 2014, could be a day that changes Australia forever.

The threat of a so-called lone wolf attack has been casting a shadow over the nation since the terror raids in September when 15 men were arrested over an alleged plot to behead an Australian and share the terror via social media.

TERROR TARGET: Why Martin Place has been chosen

It was alleged the plot involved abducting a random Australian, executing them by beheading in a public place, possibly Martin Place, and filming the act and posting it on social media.

Earlier this year, a report from counterterrorism policy think-tank ANZCTC (Australia-New Zealand Counter-Terrorism Committee) stated that any place or event which attracts a large crowd has already been identified “as attractive targets for religious and political extremists, as well as disgruntled or mentally impaired individuals.”

USED BY EXTREMISTS: What is the Black Standard jihadist flag?

But the committee is particularly concerned at the way terror organisations such as the Islamic State are urging “lone wolf” attacks against the West.

The reason is simple: Such acts by individuals or very small groups are incredibly hard to detect and prevent.

Australian intelligence services have long believed a stand-alone bomb, blade and firearm attack by radicals living within Australia is the most likely threat scenario faced.

While access to guns is highly regulated here, the prospect of a lone gunman wreaking havoc “is still considered to be one of the most likely methods of attack,” the ANZCTC document states.

History appears to support this. In 2009, four men were arrested over a plot to attack the Holsworthy Army Barracks in NSW. They had planned to enter the base and shoot as many soldiers as they could.

The “wolf pack” is also eminently possible: The shadows of the horrific Westgate Mall attack in Kenya and the beheading of soldier Lee Rigby in London loom large.

A gun, knife or bomb attack — be it by a disturbed individual or a small group of ideologically-driven terrorists — usually has only one goal: To kill as many as possible, as quickly as possible.

And to send a message.

This is why Australia’s recent terror alert was directed at public places, facilities and events. Any crowd offers the best opportunity to achieve carnage and attention. Especially if the venue seems to be a “soft target”.