The Ministry of Health is denying it did not take warnings about a damaging computer virus seriously enough.
The virus is thought to have infected more than 15 million computers worldwide and originated from the Ukraine.
It attacked internal email services at the Ministry of Health and forced it to take its websites offline.
Internet New Zealand said the worm, known as Downadup, Conficker or Kido, affects only Microsoft Windows programmes and the ministry delayed applying a security patch to its network.
In October, the government agency for computer security, the Centre for Critical Infrastructure Protection, issued a warning to all government departments about the virus.
But Alan Hesketh, of the ministry's information directorate, said acting on the initial warning would have meant closing the ministry down for at least two full days.
Mr Hesketh said it was a question of balancing the risk of putting the operating system changes in while keeping the business running.
The virus has been destroyed, but personal internet use at the ministry is not available for the time being, as a precaution.
Health Minister Tony Ryall was unavailable for comment on Monday.
Internet New Zealand said most internet users should not be affected by the virus, as long as they have taken simple precautions, such as ensuring that virus-checkers and firewalls are up to date.
