Last Friday in a media conference with Attorney-General George Brandis, Prime Minister Tony Abbott announced that the Australian terror threat would be raised from medium to high, meaning that a terrorist attack is “likely”.

In spite of this, the PM noted that there was no “specific evidence” of a terrorist attack and told us to go about our lives as normal. Crikey explains how what the high alert means and what might happen in the foreseeable future.

What is ‘high alert’?

Australia has a four-level system of alerts for national counter-terrorism: low, medium, high and extreme. This is the first time the terror alert level has been raised to “high” since the introduction of the system in 2003. Since its introduction, the alert level has consistently stayed at medium, signifying a terrorist attack “could occur”.

What does the announcement mean for everyday Australians?

The increased terror threat means that in some areas you may see a heightened level of security. State premiers have told us to expect more police at public events, plus greater security checks at transport hubs like bus and railway stations, airports, military bases and government buildings.

But the government emphasises that there’s no reason to stay away from public places or change your normal routine. Travelling overseas for work or holidays will not be a problem and exercising cautionary measures for international travel to certain countries will continue as normal. Experts say that levels of security will depend on where you are in the country, meaning that certain cities might have different levels of security.

Public places known to gather a crowd could be most vulnerable, so expect to see higher levels of security in key areas such as the Sydney Opera House or the MCG during the footy finals.

Are we the only ones with a high terror alert?

The United States did away with its colour-coded system of terror alerts in 2011 in favour of the National Terrorism Advisory System, which issues alerts in anticipation of specific threats. While the colour-coded system was in place, from 2002-2011, the level vacillated between elevated (yellow) and high (orange). It once was raised to severe (red), when British intelligence agencies intercepted plans to blow up an aircraft. Currently, in spite of an announcement by US President Barack Obama that the US intends to to “degrade and destroy” IS, counter-terrorism officials believe that Islamic State militants are not capable of carrying out attacks on US soil.

In the United Kingdom, the terror threat currently sits at severe, meaning a terrorist attack is highly likely. Islamic extremists based in the UK have contributed to the current situation and there have been several terrorist attack plots in the UK planned by residents. Britain has so far resisted calls to join the US coalition to launch airstrikes against IS, although Prime Minister David Cameron said he will not rule out this option.

Currently, Australia is the only country that has committed troops to the US coalition, with 600 troops and eight fighter jets to be deployed to the Middle East in an operation that could take “many months”. The French Foreign Minister declared on Friday he would take part in airstrikes if necessary.

How long will we be on high alert?

The Australian National Security website states that it is likely we will be living with increased security for the “foreseeable future”, though Abbott suggests that it could return to lower levels if the current threat reduces.

What form could a terrorist attack take?

ASIO’s Director-General David Irvine said the threat could manifest itself in a number of ways, including a bombing reminiscent of the Bali nightclub attack in 2002, or other attacks from loners and small groups.

Is this related to that metadata thing I’ve been hearing about?

There’s also talk of the government bringing in new laws to target foreign fighters as well as giving security agencies increased powers such as additional access to phone and computer records. But agencies have been pushing for data retention and other additional intelligence gathering powers now for several years.

What is next?

A public awareness campaign about the increased terror threat is expected to be launched in the coming weeks, and Abbott has advised people to report any suspicious activity to the national security hotline.

On the whole, the heightened alert level is probably best summed up by Queensland premier Campbell Newman, who issued a series of dramatic tweets on Friday afternoon urging Queenslanders to look out for things that are “out of the ordinary”, warning that “Intelligence agencies are hearing of individuals discussing potential criminal acts” and that there’d be a greater police presence at public gatherings. But then, as if Newman and his staff had realised people might be more reluctant to holiday or go out in public in Queensland because of his warnings, he added “there is no need to change your plans”.