The increasing involvement of spy agencies in fighting crime is "alarming", says investigative journalist Nicky Hager.

The Government Communications Security Bureau has provided "support of the prevention or detection of serious crime" 16 times in the past year alone, a request under the Official Information Act has revealed.

The GCSB has previously said it has investigated 58 cases where it has provided assistance to law enforcement agencies.

One of those investigations - that into internet mogul Kim Dotcom - was the subject of an inquiry by Paul Neazor, the Inspector-General of Intelligence and Security.


"The reason it's got the extraordinary powers that it has to spy on everyone all the time is because they are supposed to be doing the most dire threats against the state," Hager said.

Evidence from the GCSB couldn't be questioned in the way that police evidence was, he said.

"When the police do it to bug cars it all comes out in court. Quite often we know the police haven't done it right or evidence wasn't and they have to open it up."