That's what the High Court has posed to lawyers for journalist Annika Smethurst, who want a warrant federal police used to raid her Canberra home and take data from her phone earlier this year to be quashed.

Smethurst's lawyers are asking the court to rule on whether the warrant was invalid because it either misstated or did not precisely state the alleged offence, and whether it infringed the implied freedom of political communication.

It's unknown what police copied from her mobile phone, or what information the magistrate who issued the warrant was provided in order to give it the tick of approval.

Smethurst's lawyer Stephen Lloyd SC said if the warrant was invalid, then police were trespassing at the journalist's house and in her phone.

The News Corp journalist was forced to tell police her passcode before they accessed her phone and copied information to a USB which they had brought with them.

If the warrant is invalid, then police should not be able to hang onto the USB for potential criminal cases in the future, Mr Lloyd argued on Tuesday.

Ideally, police should have to destroy the device, he said.

The seven justices of Australia's highest court wanted to know why they should let either option happen, pointing to whether the information taken from the mobile phone was simply private, or confidential.

Mr Lloyd will argue that point in greater detail on Wednesday morning.

In April 2018, Smethurst published three stories in The Sunday Telegraph and online about a proposal to allow the Australian Signals Directorate to spy on Australians without a warrant.

A day later, the matter was referred to the Australian Federal Police for investigation, with officers raiding the journalist's home on June 4.

Mr Lloyd said the warrant bears little relation to any offence under the Crimes Act.

Solicitor-General for the Commonwealth Stephen Donaghue argued the warrant didn't need to provide specific detail about the offence, as outlining the section was enough.

The warrant included the date of the published story as well as Smethurst's name and The Sunday Telegraph, which it didn't have to, Mr Donaghue said.

Mr Donaghue was asked if the warrant had enough information for both the police and Smethurst to know what could be searched.

"There was quite a lot of guidance," he argued, saying the warrant clearly related to the stories.

Even if the material was seized unlawfully, the government argues police should be allowed to keep it so the question of its use can be determined in the event criminal proceedings are launched.

The information copied from Smethurst's mobile phone posed a "chicken and egg problem", Mr Donaghue said, as the police won't know if there's charges to be laid without the content.

Australian Associated Press