New South Wales Police are being given sweeping new powers to search people's homes and hack into their computers for up to three years without their knowledge.

The State Government admits police have already used the measures, even though the Supreme Court ruled the practices unlawful in 2006.

The Government says new legislation, to be introduced into Parliament today, will ensure police evidence collected using the practices will hold up in court.

Police Minister Tony Kelly says the reforms will allow police to collect enough evidence for a prosecution without tipping off criminals.

Mr Kelly says all applications for the covert search warrant will have to go before a Supreme Court judge.

He says a judge would initially authorise the search to be kept secret for up to six months but police could apply for notification to be delayed for up to 18 months, or three years in exceptional circumstances.

"For particularly anybody who's involved in crime or criminal activity, the police will now be able to undertake investigations and gather evidence before you know it," he said.

"So anybody who's involved in serious crime, the police will now be able to get on to you, even go into your computer."

Police have welcomed the new laws but Australian Council for Civil Liberties president Terry O'Gorman says they are open to abuse.

"Clearly, if the police are able to search a person's home without anyone being present, the police will be in the position to plant evidence," he said.

"That's a big worry. This particular announcement today extends police powers hugely without putting in any checks and balances against those powers being abused."

The laws will apply to offences punishable by at least seven years' jail, including drugs and firearms offences, homicide, kidnapping, assault, money laundering, hacking, organised theft and corruption.