DrInfo was used by 60% of the country's medical centres, in 600 practices, covering ''several million patients'', Mr Jacobs estimated.
Police had handed the investigation to its national cyber crime unit, but Mr Jacobs was unaware how long the investigation might take.
He ''had heard some speculation'' about the possibility of Southern involvement in the hacking, but ''at the moment, we just don't know''.
Dr Abbott said when contacted he, too, was aware of the concerns of some in the Southern medical fraternity but he ''couldn't speculate further'' on a Southern connection.
''The good news out of this is that no [patient] information was actually hacked,'' Dr Abbott said.
One Dunedin health practitioner, who did not want to be identified, claimed a group in the South had attempted to hack the database, not necessarily to access individual records, but possibly to cause issues for DrInfo.
Dr Abbott said the attack was unusual, in that it was ''sustained, of significant size and appeared to be originating from within New Zealand''.
''Nevertheless, we encourage you to ensure that your passwords are advanced and not simple to guess,'' Dr Abbott said in his warning letter to health professionals.