At least three Tauranga schools were sent private Novopay information, after it sent personal pay information of teachers to the wrong schools.
Merivale School received the pay information from a school in Auckland on Thursday morning, a mistake which made principal Jan Tinetti question the security of her staff's details.
"Absolutely everything to do with their pay we could actually see it."
Despite the issues which have plagued Novopay from the beginning, Mrs Tinetti said the privacy breach was a "massive surprise".
"My initial thoughts were, 'Gosh that's really bad for the school we were seeing the details of', and then it suddenly hit me: 'What about my details? What's the security around that?'
"So yes, I am worried because that's a massive breach of privacy. I was worried for my staff and I've had to let them know that somebody else may or may not have their details."
Gate Pa School principal Richard Inder, who received pay details of another school, said the incident was unusual.
"We'd been seeing a lot of gains in efficency and accuracies in Novopay."
He said most teaching pay levels were well known because of the collective agreement, and his school was not sent any additional personal information such as addresses, date of birth or bank accounts.
Bethlehem School principal Brian Field said he was made aware of the personal information being sent to his school at 9am on Thursday.
The school contacted Novopay straight away, but at 10am the information was still available.
"We notified NZEI to let them know ... I didn't know how widespread it was," he said.
Education Payroll Ltd released a statement yesterday which said it regretted and apologised for the incident.
Education Payroll chief executive Stephen Crombie said it had contacted the 10 schools whose information was made available, and were continuing to contact 530 individuals who had their pay information released to principals and administrators of other schools.
"We are working with the office of the Government's chief privacy officer regarding the privacy issues involved with the release of the incorrect information, and we are also undertaking a review to ensure that this problem does not happen again."
Novopay is a web-based payroll system for state and state-integrated schools in New Zealand, processing the pay of about 110,000 teaching and support staff. It was purchased by the New Zealand Ministry of Education in August 2012. From the outset, the system led to widespread problems with more than 8000 teachers receiving incorrect pay.