Waikato District Health Board says a computer virus that shut down its entire system in December got in because its virus protection software could not eliminate the threat.
The DHB shut down 3000 PCs leaving its five hospitals and 5800 employees without computer access for two days. The virus entered the system through a USB stick.
DHB chief executive Craig Climo says weaknesses in the DHB's system enabled the Conficker virus to spread.
Three reports into the incident have been presented to the board.
Mr Climo says issues of IT infrastructure soundness are being addressed. He says USB sticks are banned from use on the DHB network.