Online activist group Anonymous hacked New Zealand Foreign Minister Murray McCully's private e-mail account and used it to sent messages mocking him, it was reported today.

The group breached McCully's e-mail account last April after New Zealand passed laws cracking down on illegal file-sharing and threatening to disconnect repeat offenders from the Internet, the Dominion Post reported.

While the hacked e-mail was a private account, McCully had asked his staff to forward official e-mails to it, the newspaper reported.

Prime Minister John Key told the Dominion Post that he was aware of the security breach but was confident the hackers had not obtained any sensitive information because if they had "it would be out (on the Internet) by now".

Key said the high-security government e-mail system that ministers use for offical communication had not been compromised.

"They were forwarded on from the official system, but it was not about the ministerial services e-mail system," he said.

McCully declined to provide details of the mocking e-mails that were sent from his account, saying: "I don't want to give people ideas."

He said he was now more careful about Internet security.

Anonymous briefly knocked down the FBI and US Justice Department websites last month after the founder of file-sharing site Megaupload, Kim Dotcom, and three associates were arrested in New Zealand.

A loose-knit collective of online activists, Anonymous has also claimed credit in recent weeks for disrupting the Central Intelligence Agency and French presidential websites.

It also released a recording earlier this month of a conference call between the FBI and Scotland Yard discussing operations against the hacking collective. (AFP)