The Inland Revenue Department says the latest telephone phishing scam is unusual because it's still generating about 200 complaints a day despite media publicity that typically causes these types of scams to disappear.
Over the past two weeks, the IRD has received complaints from some 3,000 customers and has confirmed reports of at least two people following the scammers' instructions.
IRD general manager of customer services Eleanor Young said it's impossible to know how many other people have been contacted by the scammers that haven't laid complaints. Even IRD's own staff have been targeted.
The scam calls are being made to landlines and mobile phones with messages left on voicemail if the calls remain unanswered.
People are told in a threatening and intimidating way by both male and female callers that they are from the IRD and that the customer is either wanted for historic tax evasion or fraud, there is a red flag on their file, or they are in debt, and that they or their lawyer must return the call as soon as possible.
Customers have been told they need to pay what they owe the IRD by way of iTunes vouchers or face immediate arrest.
In a case that featured on Television New Zealand's Fair Go, one man paid more than $8,000 in iTunes vouchers to the scammers who had told him he would be prosecuted if he didn't pay up.
Young said she hadn't heard of scammers demanding vouchers before and wasn't sure how they would be converted to cash.
"Obviously the IRD doesn't accept payment by way of iTunes vouchers," she said.
Another unusual feature of this scam is the volume of customers rung and that people are still being hounded even when they have already answered the call.
People are told to ring a Wellington or Auckland number to arrange immediate payment.
Customers that have rung the numbers have reported the calls have foreign-sounding accents and Young's personal view is that the scammers are based overseas.
She said as soon as the IRD, working with the telecommunications companies and police, shuts down one of the numbers left by the scammer, new numbers are given to those contacted.
Obviously the IRD doesn't accept payment by way of iTunes vouchers.
Her advice to those receiving these fake threatening calls is to hang up immediately rather than getting "hooked into the story".
IRD has a link on their home page to a list of scams that the department is regularly hit by and the tell-tale signs to look out for. One of those is the phone number, as IRD only requires customers to contact it via an 0800 number and never asks for credit card or bank account details by telephone.
Anyone being investigated for tax fraud would be interviewed in person and have been asked to provide documents rather than being accused over the telephone, Young said.
In other recent telephone and email scams, IRD customers have been told they will get a tax refund if they provide their credit card details and another sent people a link to a false website where they are asked for money and to provide personal information.