The Criminal Bar Association is confident there was no malicious intent on the part of a defence lawyer, who's caught in the middle of a massive police blunder.

A mistake at the Organised and Financial Crime Agency has caused top-secret files with details of confidential informants to be sent out accidentally to the criminal underworld.

Association president Tony Bouchier said the information was encrypted, in an email from police to the lawyer.

"I tend to believe that story because I don't think any lawyer, if they discovered that sort of level of intelligence - they would understand the significance of it and they wouldn't be passing it onto their client in any event."

The Weekend Herald reports the "stunning bungle" saw the information copied and widely circulated among gang and methamphetamine-producing circles and led to police taking emergency steps to protect those exposed by the blunder.

Last night, Assistant Commissioner Malcolm Burgess said the information had been mistakenly included in material sent to a lawyer acting for someone arrested in an investigation by the Organised and Financial Crime Agency of NZ (Ofcanz).

"Police deeply regret this mistake, which was the result of human error. Steps were taken to recover the information as soon as police were aware of the error.

"However, by this point it had been more widely circulated. Police also took other appropriate measures needed to prevent harm to any person arising from the mistake."

Police say the information was sent by mistake along with material which went to a defence lawyer.

They won't discus the content of the information because it's so sensitive.

Barrister Ron Mansfield, who has defended a number of cases investigated by Ofcanz, also noted the nature of the material bringing together different streams of intelligence.

"There's no way we would get disclosure of this. It could lead to destruction of evidence if people think they have a connection to these people or phone numbers. I don't think [the police] would be very happy at all."