Microsoft New Zealand and NetSafe say there's been a "significant increase" in reports of scammers trying to rip people off by claiming there's something wrong with their computer.
Netsafe's executive director Martin Cocker said the scammers try and legitimise their ruse by claiming to call from Microsoft.
The cold callers offer to fix compromised computers and ask for remote access to computers which can reveal credit card details or bank account numbers. Some people have allowed access and one is reported to have lost around $5000.
Mr Cocker says this pattern of scamming is not new and the scammers use the Microsoft brand as the company is known to have trusted experts.
"Unfortunately some people believe the calls are genuine and are led to believe they are doing the right thing by handing over private passwords or details. They can find themselves losing money or ending up with a computer infected with viruses or other malware that compromise their security," Mr Cocker says.