The Ministry of Social Development (MSD) is making no apologies for its processes around benefit fraud tip-offs - of which they receive one an hour everyday.
The figures obtained by Checkpoint under the Official Information Act show 8968 allegations were made in the 2016/17 financial year, resulting in 5992 investigations.
About 600 of those investigations - or less than 10 percent - were prosecuted, MSD deputy chief executive of service delivery Viv Rickard told Checkpoint with John Campbell.
The calls they received about fraud were about 3000 or 4000 more than the number of investigations, he said.
However, an overpayment that needed to be paid back was only identified in 20 percent of cases - or 1829 of them - meaning 4163 people were needlessly subjected to an investigation.
Mr Rickard emphasised the gap between the number of investigations and prosecutions showed they carefully considered cases before making a decision to act.
"We don't have to prosecute every person we overpaid, if we found a fraudulent behaviour we will take action," he said.
"I don't make any apologies for trying to look after government and taxpayers' money. However, I think the key issue is 'are we assessing information that's coming through to us appropriately?'
"I've got assurance today that we are, that we have a robust system in place."
Beneficiaries can be reported for fraud on an anonymous tip-off line to the ministry.
Lawyer Frances Joychild QC acted for a beneficiary who won a case against MSD who claimed she owed $109,852 because her bank loans and credit cards constituted income.
The original allegation against the beneficiary was made by an abusive ex-boyfriend.
Ms Joychild said it was not an isolated case and she had heard similar ones too.
Mr Rickard told Checkpoint he was confident they had the right systems in place to effectively filter those tip-offs.
"In terms of the information itself it has to be assessed, you have to think about the motives you have to be objective. Of course, there's some vindictive behaviour that occurs ... [but] I'm confident we've got the right processes in place to assess [that information].
"We're actually prosecuting a small number, of the information that we receive.
"We resolve a lot of them without going through any lines of prosecution, that's what you'd expect us to do."
MSD was changing its approach compared with previous years in response to continuous criticism, he said.
"What we're trying to do is change the way we do our business - we're trying to have a more caring approach in looking after our clients," Mr Rickard said.
"I know we are dealing with some of these issues from years gone by, we're starting to think about the organisation moving forward."
