Kim Dotcom says he is taking new court action after discovering the government may have spied on him for two months longer than it previously admitted.

Photo: RNZ / Kim Baker Wilson

The internet businessman, who faces extradition to the United States over accusations of copyright fraud, said a High Court judgment released last week revealed the GCSB spied on him until 22 March, 2012.

In affadavits the government has previously filed in court, it said it only spied on Mr Dotcom until 20 January, 2012 - the day Mr Dotcom was arrested in a dramatic raid at his Auckland mansion.

The government acknowledged later that year its spying was illegal, as Mr Dotcom was a New Zealand permanent resident and should have been exempt from GCSB surveillance.

In a live internet broadcast on Periscope this afternoon, Mr Dotcom said he would be taking action over the new information.

"My lawyers are going to file new filings with the court, because we will seek the truth."

The government had lied to the court and the new action could include a perjury case, he told RNZ.

It also made then-Prime Minister John Key's apology to him over the illegal spying "a sham".

"It tells us that the surveillance continued even after they already knew that what they did was against the law."

The GCSB found out in February 2012 that its surveillance was illegal, he said.

"The whole story that was spun, that this was really an error ... this whole narrative would have died with the real dates if we had known that this went on to March 22 - or even just until mid-February when they had internal discussions about how this was illegal."

The additional spying took place while he and his co-defendants were remanded in prison, Mr Dotcom said.

"Why would you put people that are members of a conspiracy together in the same cell block in the same jail, so they can meet and talk?

"Now it all makes sense, because the government was still spying on us... They were there with us, they were there in our cells while we were talking."

The new dates also included a period after he had been released on bail, Mr Dotcom said.

"[The spying] would probably have included the privileged communications between us and our legal teams."

Mr Dotcom's lawyer could not immediately be reached for comment.

Last year the High Court upheld a district court ruling that Mr Dotcom was eligible for extradition. Mr Dotcom is currently appealing that decision to the Court of Appeal.