Internet watchdog Netsafe is warning of cold-calling scammers ramping up attacks on New Zealand computer users.

Increasing numbers of people are reporting being called by scammers claiming to be from an IT support helpdesk.

The caller goes on to either plant malware on their computers or obtain credit card details with an offer of free computer fixes.

Netsafe Executive Director Martin Cocker says people should hang up as soon as they feel a phone call is suspicious.

"It's been reported to us that the scammers have become increasingly aggressive towards people when information isn't passed over straight away. We advise that you don't let it get to this point and hang up immediately."

Scammers offer personal detail about the victim such as a date of birth, address and even purchase history, says Mr Cocker.

That information is stolen from websites to make the the caller seem authentic, he says.

He sees the scam as a progression of the "Nigerian Lottery Scam" which fooled many into sending their bank details out by email.

"Someone over the phone sounds more legit and people are tempted to trust them, more so than an email. It concerns us that people are trusting of a call centre making outward calls.

"We would urge you to hang up, and most importantly do not offer any information of your own, or allow them to remotely log into your computer."

Ministry of Consumer Affairs spokesman Richard Parlett says reported cases of telephone scams in Australia have recently jumped from about 200 to more than 2000.

A similar increase is now being seen in New Zealand.

He is urging people to treat their computer like a bank account.

"In the same way as your bank account, don't open your computer up to anybody who asks nicely over the phone."