The Privacy Commissioner says he is troubled that confidential personal records of people in state care as children became publicly available.
The files transferred to Archives New Zealand in 1989 include names, referrals for psychiatric evaluations, prescriptions and caregivers' details.
John Edwards said it was not clear how many people may have accessed the mainly administrative files.
He said it was a more limited disclosure than might have first been suspected because they were not case files, but the administrative files incidentally recorded some details of people's interactions with the agency.
"At this stage I'm not sure that there's any way of knowing how many, if any, people would have had their eyes on those documents. I mean they were probably not of great interest to most of the public who uses the archives and certainly we've seen no evidence that the information has been widely distributed.
"It's as if a door's been left open but we don't really know how many people have gone in and then looked at the information."
He said he hoped that people were not unnecessarily distressed because the information was administrative rather than their detailed records and it was probably not a widespread disclosure, although "it was a troubling vulnerability".
Mr Edwards advised that anyone who was worried about this should firstly get in touch with Oranga Tamariki to see whether their records had been exposed.
If they had been, and it continued to trouble them, they could try and work that through with Oranga Tamariki and if that failed then they could get in touch with the Privacy Commission which would look at it, he said.
Mr Edwards said that having spoken with Archives and Oranga Tamariki he is satisfied this was a one-off case.