NSW Police has refused to reveal if defence lawyers are being spied on with electronic surveillance as part of criminal investigations.

Key points: Police Commissioner Mick Fuller has provided a written answer to a spyware question at Budget Estimates, saying "it is unclear from the question what 'spyware' refers to"

Police Commissioner Mick Fuller has provided a written answer to a spyware question at Budget Estimates, saying "it is unclear from the question what 'spyware' refers to" Security insiders say NSW Police has a licence for Finfisher, a powerful "spyware" software

Security insiders say NSW Police has a licence for Finfisher, a powerful "spyware" software Greens MP David Shoebridge has called the Commissioner's response "contemptuous"

Police Commissioner Mick Fuller was questioned at Budget Estimates if his officers deployed spyware to monitor criminal defence lawyers through their mobile phones and other devices.

Initially he elected to take questions on notice — citing operational concerns.

Later, in a written answer, Commissioner Fuller declined to answer and instead told NSW Parliament: "It is unclear from the question what 'spyware' refers to."

Security insiders have told the ABC that the NSW Police has a licence for Finfisher, a powerful software tool sold by an international company called Gamma International, and marketed as "spyware".

Commissioner Fuller declined to answer questions and instead told Parliament: "It is unclear from the question what 'spyware' refers to." ( ABC Brisbane )

Governments and law enforcement agencies use the software to infect laptops, tablets and smartphones of surveillance targets, such as outlaw bikie gangs, terrorists and drug smugglers.

Once a device is infected Finfisher can secretly switch on cameras and microphones to monitor targets — operating even when devices are powered down.

Commissioner Fuller broadly defended the use of high-tech surveillance for operations which required a warrant.

"We cannot use those sorts of powers without a legal right," he wrote.

Shoebridge labels response 'contemptuous'

NSW Greens MP David Shoebridge, who put the questions to NSW Police, has criticised Commissioner Fuller's written response as "contemptuous" and lacking transparency.

"The Commissioner needs to come out and either say he's not using it, or if he is using it, how it can be done without trespassing on a key legal protection," Mr Shoebridge said.

"You'd think at a minimum he would have put in detail what those legislative requirements were."

The questions over breaching client-lawyer privilege in New South Wales come as a Melbourne barrister has been revealed as a police informer, with the approval of senior police.

Finfisher has attracted controversy over its use by repressive regimes in Egypt and Ethiopia against democracy activists.

Mr Shoebridge said defence lawyers were increasingly fearful about using their mobile phones.

"That level of concern rises as the seriousness of the criminal matters that they are dealing with increases," he said.