Police have this week been inundated with calls reporting a phone scam impersonating police officials asking for name and IRD number.
Netsafe technology director Sean Lyons said although the scammer appeared to have a Kiwi accent, it was probably an overseas-based operation running the scam.
"Scammers are catching on," Lyons said.
"These organisations are not small or stupid. They know now not to speak in Indian or Middle-Eastern accents, because that's the feedback they've been getting. Now they either work on their accents, or use voice grabs."
He could not say if anyone had fallen for the scam but said the calls coming in were "just the tip of the iceberg".
A police spokesperson said reports of the scam starting coming in about midday on Tuesday. The scammer sounded like a Kiwi and was telling people they owed money to Inland Revenue, instructing them to contact the number provided or face arrest.
It was important to remember that government agencies never contacted people to ask for bank account or credit card details over the phone.
Anyone who has received a call similar to the one described is advised to contact local police.