Early investigations show the funds have been sent to Australian bank accounts, while the New Zealand Bankers' Association is reminding people that banks would never ring and ask for personal information over the phone.
Spark's general manager of care Bridgette Dalzell said Spark would never call customers out of the blue to ask for personal details such as a bank account number, or credit card or internet banking details.
"If you receive a call from someone claiming to be from Spark who asks for your personal information, end the call immediately."
Auckland woman Joan, who asked that her surname not be published, told the Herald she had received several calls from people pretending to be from Spark over the past six months.
She had been called twice in the past two weeks, but was now quick to hang up when she recognised who was calling.
"They say: 'This is Spark ringing about a problem with your computer'. They kept wanting me to press this and press that, but I'm not very good with the computer, us older folk,'' the 83-year-old said.
The first time they called, they warned her internet and phone connections would be cut off by 5pm if she did not carry out what they asked her to do on her computer.
However, her machine - a Mac - did not have the Windows-settings they were more familiar with.
The pensioner said she felt threatened and worried that other elderly people would feel the same way.
"I couldn't do what they wanted me to do and I was getting so worried.
"I've got a medical alarm and my blood pressure was going up - they were scaring the living daylights out of me.''
After speaking with her son, they contacted Spark to report the matter and were told the company was aware of the situation.
The best advice was to immediately hang up and contact Spark directly. She has also started telling friends of hers to be alert about scammers.
"The last few times they've called again, I just hang up - they're not getting past this old girl,'' Joan said with a laugh.
Bankers' Association chief executive Karen Scott-Howman reminded people not to give out bank account usernames, passwords, PINs or verification codes.
"While your bank may ask questions to confirm your identity, it will never ask for this confidential information.
"If in doubt, just hang up and call your bank's 0800 number to report the call."
Scott-Howman said a utility service provider would never call a customer and then transfer them to a bank.
She said a bank will never ring and ask personal information over the phone, and urged people not to give any sort of password to anyone.
A police spokesperson said anyone who calls and asks for financial information shouldn't be trusted.
Police advise anyone who gets such a call to hang up, call the company on their published 0800 number, or arrange a meeting at the relevant agency branch.
Anyone who believes they've been targeted by the scam should report it to the Consumer Protection Scamwatch website, at www.consumerprotection.govt.nz/get-guidance/scams-and-online-safety/scams.
