Aggressive foreign scammers are again targeting New Zealanders, this time by urging them to change settings on their computers in an attempt to obtain personal information.

Within the past two days, hundreds of people have received telephone calls from people claiming to be Microsoft employees or from IT companies in Dubai and NZ warning that their computers could be infected with a virus.

The caller - a man or a woman with a foreign accent on a poor line - asks for passwords, which they claim they need to get rid of the virus.

In some cases the caller has become aggressive and defensive when challenged by those who don't believe the story.

Police say anyone who receives such a call should hang up.

Tauranga woman Anita O'Connor said she answered a call from a woman with a thick foreign accent who told her she'd had an error message from her computer.

"She said she was from an IT support company and that I needed to go to my computer now."

Ms O'Connor told the Herald the caller said "do what I say", but instead she challenged her by again asking where she was from.

"The more I kept stalling the angrier she got. I asked her if she could tell me who my internet provider was and she said, 'it's not important'."

Ms O'Connor said she would call her back and requested her name and number, but the woman hung up.

Aucklander Brian Thomas had a similar call, from someone claiming to represent a company in Waitakere - although the caller could not pronounce "Waitakere" properly.

The caller told Mr Thomas his computer had a virus.

"He wanted me to go to my computer and follow his instructions to rectify the 'problem'."

Mr Thomas had other ideas though. "I had some fun first winding the loser up before he got annoyed and hung up on me."

The Ministry of Consumer Affairs's "Scamwatch" advises being "very wary" about giving out PC details over the phone to strangers.

Spokesman Richard Parlett said Scamwatch had noticed an increase in the number of scam bids being made in phone calls, rather than emails.

"It can be a lot harder to put the phone down then to hit delete," Mr Parlett said.