Police are warning landline users about a surge in people being conned out of thousands of dollars by phone scammers.

Three men in Auckland, aged in their 20s and 30s, have been charged in relation to alleged money laundering after an 84-year-old victim lost almost $10,000 after getting a phone call from someone pretending to be from Spark.

The way it works according to the police is the caller then manipulates the victim into unwittingly allowing them remote access to their computer and bank account. Det Snr Sgt Bridget Doell says the scammers are likely locals, working for an offshore entity.

"There's a variety of ways that people are scammed and it is generally the same method, probably globally. People are contacted on their phones, mainly landline phone numbers, and we believe from some investigations that we've done in the past, mainly from offshore scammers, and they managed to manipulate who they call to access their computer through a TeamViewer app which gives the scammers access to their accounts. And that's where it starts."

One example of the scam is people being told that if they don't give access to their computer to fix their email, then they will lose all email access.

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"They pretend to be from reputable companies, Microsoft, Spark… They use a dialing app, so they probably just call many, many random numbers in New Zealand."

Often victims are the more vulnerable, the elderly, that are at home during the day and still have landline phone numbers.

"They claim they're from Spark, and they need to click on a TeamViewer app. Once the scammer guides them to that… and that gives the scammer access to the computer and access to their accounts.

"The victims that have been called don't realise that is actually the case and money starts to be moved from their accounts on the computer online."

Doell said earlier in the year someone lost up to $250,000.

"If anyone doubts any phone call that they have, or anyone guides them to open any applications on their computer. Just don't do it. No one will ask or ring you to do that."