A computer virus disabled the automated response system of St John communication centres across the country this week.
Ambulance communications operations manager Alan Goudge said systems were back up and running yesterday morning after being attacked by the virus on Wednesday night.
The incident forced staff to allocate ambulances manually but it is still unknown if any emergency call-outs were affected.
"Anti-virus software protected the systems but as a result of the virus it impacted on some of the systems services, mainly those related to paging and radio. Back-up systems immediately took over when it was detected and the workload was managed manually," Mr Goudge said.
Mr Goudge said the source of the virus was still being investigated. "While it has now been contained we are looking into how and why it entered our system."
A Hamilton IT expert, who did not wish to be named, said he was surprised by the outage in an emergency call centre and said he expected a robust system to be heavily protected by computer security systems.
"Without forensic access to the system it's hard to gauge what went on, however in most cases a virus is transferred from a memory stick plugged into the system," he said. "One would expect a system like this to have strict controls around memory stick use."
A memory stick was responsible for introducing the Conficker virus to Waikato District Health Board computers in December 2009. The virus disabled the system for two days, affecting more than 6000 staff and thousands of patients who had procedures delayed while the problem was fixed.
When St John receives a 111 emergency call an ambulance is alerted via a mobile data terminal (MDT) linked to a paging system.
The MDT, similar to an on-board computer, displays information about the emergency, including what and where it is.
But during this week's outage, ambulance officers were in some cases called via station phones and emergency information was relayed in person.
St John had not received any reports that emergency response times were affected, but Mr Goudge said the organisation was investigating the impact the disruption had on the service.
"Any responses of concern that result from the investigations will be followed up with patients and family involved," he said.
Communication centres in Auckland, Wellington and Christchurch, that receive more than one million calls a year, were affected.
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