The Krack cyber-security threat has been overblown and public warnings to avoid using Wi-Fi are over the top, an IT security expert says.

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Both InternetNZ and the government cyber watchdog Cert NZ have urged people to avoid using Wi-Fi if they can after the discovery of a weakness that allow hackers to read data that passes between a device and the Wi-Fi router.

It affects computers, mobile phones, routers and smart TVs and telecommunications companies are racing to find a fix.

No attacks have been reported in New Zealand so far.

Here's what you need to know about the threat

Peter Gutmann, an IT security expert from Auckland University, said expecting people to shut off the Wi-Fi was unreasonable.

"That may be going a bit too far. You know I'm not going to switch to cellular data," Dr Gutmann said.

"I use the Wi-Fi at the university and yes that can in theory be attacked but anything that's sensitive [like internet banking passwords or credit card details] is going to be encrypted with a separate layer of encryption anyway.

"I'm not terribly worried about it.

He said although an attack had the potential to cause mayhem if carried out on a large scale, it was highly unlikely.

But he said businesses might need to be more careful about sharing delicate information over Wi-Fi.

"Let's say you've got a business and you've got a business competitor that wants to come in and mess around with your internal network, you need to be a bit more careful there.

"For example provide security measures if you're coming in with a cellphone so then you don't have access to all the corporate data and the spreadsheets and the accounting and financial data via a wireless connection."