A computer hacker has demanded US$5000 in bitcoin from Hāwera High School in South Taranaki.

An anonymous computer hacker has demanded US$5000 from a provincial high school to return course work they are holding for ransom.

Hāwera High School staff in South Taranaki switched on their computers on Monday to discover a message demanding payment for the return of encrypted data on a server containing students' work and teaching resources, principal Rachel Williams said.

The hack did not affect student and staff records but the entire school network was taken offline as a precaution.

Kris Boult Police have advised Hāwera High School Principal Rachel Williams against paying the hacker.

The only devices being used at the school are running off their own data or a hotspot from a mobile phone, she said.

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Forensics experts from the police, Ministry of Education and the school's network provider were all working to find the source of the intrusion.

Catherine Groenestein To protect itself Hāwera High School has shut down its entire network.

"Potentially it is pretty serious. What we've had to do is take everything offline until we get forensics done," Williams said.

"There has been an email saying we'll let you have it all back if you give us some money. But the advice from the police is not to pay the money."

Williams said a number of staff had lost work to the hack and work by students may have also ensnared.

The school was being supported by the Ministry of Education and the New Zealand Qualifications Authority to work out what information had been lost.

"It's very much a case-by-case basis, it will take us some time to work it all out with each particular student and each particular teacher and for each standard," she said.

"Some of the students who have things on memory sticks will be fine and some students save their stuff on our cloud-based system."

The hacker was likely to be from somewhere overseas.

"We've got no reason to believe it's anything other than a random thing," Williams said.

"The school has good security and our network provider manages hundreds of other schools in the country. Unfortunately we have just been very unlucky."

The principal has been buoyed by offers of practical help as well as support from the school community.

Two Hāwera computer businesses had also offered to assist with scanning students' devices and memory sticks to avoid the problem infecting computers elsewhere.

A known variant of ransomware malware had been identified as causing the issue, and inquiries were continuing into the case, Detective Sergeant Damian Rapira–Davies of the Police Cybercrime Unit said in a statement.

Deputy principal Declan Sheridan said an assembly for senior students was held on Wednesday morning to inform students about what was happening and support those who were worried about it.

"Some of it comes down to personal preference as to how they save things. Some will be 'oh that's a little bit inconvenient', some will be very upset. That's something we obviously need to manage."

In a written statement an NZQA spokesperson said its staff were working closely with Hāwera High School to minimise the impact on students and were offering support and guidance.