Worldwide activist group Anonymous is believed to be behind a hack attack on the Government Communications Security Bureau website on Friday.

On Thursday, Anonymous posted a threatening video on YouTube, claiming that Prime Minister John Key, the Act Party and veteran politician Peter Dunne were to be held responsible for the destruction of internet freedom and basic human rights of New Zealand citizens by passing the GCSB bill, "which allows your government to spy on you".

It is understood the GCSB website suffered a saturation of external communication requests, to the point where it could not respond to legitimate traffic.

The communications interception agency confirmed the attack slowed its gateway for about 30 minutes.


In the warning video, a man wearing a black hooded outfit and Guy Fawkes mask said: "We, as Anonymous have decided to take action. To the Government of New Zealand, you now have our full attention and we will be watching your every move ... this is your final warning."

A spokesman for GCSB said there could have been some temporary degradation of service.