She gave him access and could see the cursor zooming around the screen and then the pop-up disappeared. He also advised her he had installed a total security system.
The remotely located repair man then said it was time to pay the US$399, which needed to be made by credit card.
Reluctantly she gave over the number but then she became suspicious about the cost.
"I noticed it was in American dollars and queried the amount and it was over NZ$500."
That's when she pulled the computer plug from the power source.
She immediately went to the bank and had the credit card cancelled and took her laptop to a computer repair man to have it checked.
The woman said she was cautious about using her credit card online and had only done so on two previous occasions, including one to pay for an airline ticket. She was embarrassed that she had been sucked in but wanted others to be warned.
"It all looks so legitimate but if in doubt just unplug the computer," she said.
A NetSafe spokeswoman said it used to be cold calling scams which used a computer virus as a way to hack into people's computers.
But now it was not uncommon for pop-up windows, that looked very professional and legitimate, to hook people in.
"It used to be scams were easy to spot but now that's getting harder. Scammers are getting more sophisticated."
Scammers often use the names of well-known companies that specialised in computer software to gain trust.
The pop-up advertisements aim to mimic genuine warning alerts generated by computer security software.
NetSafe recommended hitting 'control', 'alt' and 'delete' to view a list of programs running on the computer and delete the pop-up alert from the list of running programs.
NetSafe praised the actions of the Whangarei woman saying she had done everything right when she realised it was a scam.
She reiterated that major companies, including banks, would not ask for bank details.
If you suspect a scam contact 0800 NETSAFE.