On Wednesday morning, Australian Federal Police officers and computer technicians entered the ABC's headquarters in Sydney armed with a warrant to access the national broadcaster's databases.

Quartered in a room with ABC lawyers and IT personnel, police categorically searched all files that might be related to a series of 2017 stories known as The Afghan Files.

They went from the specific search terms such as journalists "Dan Oakes" and "Sam Clark", to the broad — searching for the word "secret" and "Department of Defence".

At the end of more than eight hours of the police accessing and viewing thousands of files under the watch of the ABC's lawyers, the AFP downloaded about a hundred files on two USBs and sealed them into a special evidence bag.

The ABC now has two weeks to challenge the terms of the warrant as well as claim privilege over the contents of the documents before the AFP can unseal that bag and potentially use the files as evidence.

The ABC's managing director said its journalists' sources were safe.

"The ABC stands by its journalists, will protect its sources and continue to report without fear or favour on national security and intelligence issues when there is a clear public interest," David Anderson said.

But what do the raids on the ABC, and on News Corp journalist Annika Smethurst a day earlier, mean for journalists and their sources? How could the ABC's headquarters be raided? And does press freedom exist in Australia? We answer some of your most common questions.

What authority do police have to access journalists' files?

The AFP has powers to execute search warrants as part of an investigation into possible breaches of Commonwealth law.

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Lawyer and criminal justice spokesman for the Australian Lawyers Alliance Greg Barns said if a search warrant was legally served, the only option to stop it from proceeding was to apply for an injunction through the courts.

"Once they show you the warrant, they're entitled to enter," he said.

There will now be a negotiation process between police and ABC lawyers about what documents can be lawfully seized under the terms of the warrant.

The ABC lawyers could also challenge the terms of the warrant.

Acting AFP Commissioner Neil Gaughan said no sector of the community should be immune to the law.

"This includes law enforcement itself, the media, or indeed, even politicians," he said.

"There are criminal allegations being investigated and we cannot ignore them."

Why are journalists being raided now, years after publication of the original stories?

The Australian Federal Police said there was no connection between the raid on Smethurst's home on Tuesday and the ABC in Sydney on Wednesday. But both search warrants relate to separate stories and allegations of publishing classified material, under the Crimes Act 1914.

The AFP said it received separate referrals from agency heads in the days after the stories were first published in July 2017 and April 2018. Why it took until June 2019 for the raids to occur is unclear but Acting Commissioner Gaughan said these investigations were typically complex and lengthy.

"The timing of these investigations or these activities was influenced only by the progress of the investigation to date, and sufficient information being available to support the application of a search warrant," he said.

"The execution of the search warrants and the timing of the search warrants are aimed at lawfully locating evidence and seizing the elements in a manner that will withstand the scrutiny of a court of law."

The AFP responded strongly to suggestions the timing of the raids was politically motivated, saying neither the Government or any minister had directed the actions of these investigations.

ABC lawyers have been in ongoing negotiations with police over their investigation into The Afghan Files for some time.

But didn't national security laws just change?

In 2018, sweeping changes were introduced to Australia's national security laws including wider metadata surveillance powers and new secrecy offences. While the laws carry slightly harsher penalties for some offences, the amendments also include a limited public interest defence which could be used by journalists.

The AFP have highlighted they were unable to rely on the revised secrecy offences because, in both cases of the ABC and News Corp investigations, the alleged conduct occurred before the new offences were in force.

Mr Barns said that meant it could be more difficult for journalists to claim public interest protections. And the public interest test does not apply to the public servant whistleblowers.

"New laws passed last year allow for a limited public interest defence which is provided to journalists and their publishers but it does not enable the source of the material to enjoy that protection," he said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 35 seconds 35 s ABC managing director comments on AFP raid

What is being investigated?

The AFP has issued a statement saying the search warrants related to secrecy offences contained in the now-repealed parts of the Crimes Act 1914 and affects both Commonwealth public servants and journalists.

Under the act it is an offence for Commonwealth officers to disclose information without authorisation.

Mr Barns said the offences carry a penalty of up to seven years in jail under the old legislation.

"You can go to jail for long periods of time," he said.

"It sends a clear message to media organisations, journalists and sources that they are at risk if they publish information the Government doesn't want them to publish."

What protections are there for journalists and their sources?

The short answer is there are some protections, but our laws protecting sources are much weaker than they are in other comparable democracies.

Australia does not have a bill of rights or clear constitutional protections for journalists and whistleblowers like the US, UK and Canada do.

Those protections, Mr Barns said, meant journalists in those countries were able to assert a constitutional right, via freedom of speech clauses, which would prevent police from being able to access their documents.

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There are also some state and territory laws which allow greater protections for journalists and their sources, but they do not apply to Commonwealth law.

Mr Barns said the laws protecting journalists and their sources were not clear cut, "particularly in a case where it's quite obvious what the police are trying to do is find out who the source is in relation to a particular document".

"In Australia, journalists are in a more precarious position and there have been some cases where parties have gone to court to force journalists to reveal their sources," he said.

There are public interest arguments inserted into the law to protect journalists, as mentioned above, but they must be weighed against the Australian national security interests.

What will happen next?

The ABC's lawyers will now begin a two-week period of review of the sealed documents handed to police. In this time they can claim legal professional privilege over some of the documents or argue about the terms of the search warrant in court.

Once this process is over, and depending on the outcome of the court proceedings, police could use the evidence to make a case for any whistleblower alleged to have leaked the information.

"It's important to say we're in the evidence collection phase of the investigation. Now, clearly, we've got a long way to go," Acting Commissioner Gaughan said.

"Public interest is something that we look at in relation to our investigations from the outset.

"It's in the Commonwealth's Director of Public Prosecutions guideline in relation to whether or not they commence a prosecution based on public interest."