Nigerian immigration fraudsters are targeting New Zealand as a place to live and take advantage of humanitarian migration policy to bring dozens of family members with them.
The scams have cost taxpayers hundreds of thousands of dollars and led to an investigation of 160 residency applications, which found more than a quarter were fraudulent.
Prison sentences for three men were publicised as separate cases but Weekend Herald inquiries reveal the existence of a wider operation which led to residency applications for the men and family members to be declined.
Operation Naira, which is codenamed after the Nigerian currency, began in 2009 after intelligence from officials in London suggested immigration applications from the West Africans were "high risk", particularly around secondary migration sponsorship.
The wide-ranging probe reviewed 160 cases and exposed the problems New Zealand authorities face combating immigration fraud.
More than 40 residency applications were declined, with eight people arrested and charged. The review is on-going with investigators now turning their attention to those who have already been granted residency, or citizenship.
One of the three men jailed, Chidozie Emmanuel Onovo, was working as a hospital psychiatrist in Christchurch when he was found to have falsified documents to hide a British drug-smuggling conviction.
Another, Hakeem Amoo Ewebiyi, was working with sex offenders for a community health provider when he was discovered to have entered the country on a false South African passport.
The third, Jeffrey Ugochukwu Orji, is an engineer who unsuccessfully sought refugee status in New Zealand 10 years ago before returning on a false passport a year later.
The charges against two others were dropped but their residency applications were declined. Three other cases are still before the courts.
The 43 declined residency applications are mostly family members of the eight charged, relatives who attempted to gain permanent access to the country through the secondary migration policy.
The cost savings from preventing fraudulent secondary migration, where a principal applicant successfully acquires residence and as a result helps other family members to come here, are significant.
"It has been estimated that on average each refugee fraud conservatively costs the Department of Labour $28,550," says a 2010 Labour Department report.
This does not include the "downstream" cost to the taxpayer of legal aid, healthcare, education, state housing, welfare, police and courts.
While Operation Naira was successful in stopping others from being granted residency, the investigation also raised questions over the adequacy of the vetting system.
The sweeping inquiry came soon after an Auditor-General's report in 2007 criticised Labour Department handling of identity fraud detection and highlighted the inadequacy of risk identification at the time.
The Auditor-General made 15 recommendations, all of which the Minister of Immigration ordered to be implemented.
These included the need to identify, monitor and address risks specific to immigration fraud and greater training for frontline staff assessing applications to detect dishonesty.
Sophisticated passport scanners to detect forgeries have since been introduced at airports, as well as pre-screening processes which have decreased asylum claims from a peak of 2000 each year to 300.
But the Labour Department says the introduction this year of biodata technology at the border, capturing photographs and fingerprints, now gives New Zealand the "single most effective tool in countering identity fraud".