Council chief information officer Graeme Riley said the research company informed the council and its other clients, including the NZ Police, late on Wednesday that it had been affected by a cyberattack.
The scope of the breach was still being investigated and it had not yet been confirmed whether the survey information collected on behalf of the council was affected, but the company was investigating.
The attack had been reported to police and the Privacy Commissioner.
The research company had just completed its first year of residents’ opinion surveying for the council.
Residents were randomly selected from the electoral roll and invited to complete the survey — about 1200 people did so in the past year.
Survey participants use the survey to rate their satisfaction with council services and facilities.
The survey was the only information the research company collected on behalf of the council, Mr Riley said.
Police said on Wednesday they was investigating the possible hacking of the research company.