Retail NZ says it is "disappointing" some retailers had to deal with aggressive customers during the global IT outage.
Global services are slowly recovering from a crippling software update issued by cybersecurity firm CrowdStrike on Friday (NZ time).
Airlines, healthcare, shipping, finance, TV networks, transport networks and more around the world were affected by the faulty update, which crashed Microsoft Windows-powered computers so badly they could not be easily restored with a simple restart.
In Aotearoa, more than half of Retail NZ's members were affected, said chief executive Carolyn Young. Some members had reported "aggressive customer behaviour", which she told Saturday Morning was "disappointing".
"People were getting quite agitated about the fact that payments weren't going through, knowing that they had money in their account and especially earlier on in this phase when people weren't aware that the banks were out and it was a global issue."
"There were people at the supermarket and various other places where they're trying to purchase items that they wanted for that evening and they couldn't do that. So they were frustrated, and unfortunately their frustration came out in an aggressive and quite confrontational conversations with retail staff."
Young's advice to retailers open on Saturday was to check their systems and make people aware of any potential issues as they came into the store.
Eftpos stayed online during the outage, and she also recommended retailers ensure that was the case for their business.
"There's an agreement with the banks around how the Eftpos transactions can work in an offline mode and so, retailers may need to get in touch with their terminal providers to make sure that is all set and appropriate but Eftpos or cash are more likely to have a complete transaction than some of the contactless transactions which is where you've got it going through different gateways.
"Cash is king, and then Eftpos would be second."
Young said the incident revealed how reliant businesses were on technology and how interconnected everything was.
Woolworths back up and running
Meanwhile, Woolworths NZ said all its stores reopened Saturday morning, but some checkouts were still affected and online shopping was not yet available.
About a dozen of its stores had to close their doors on Friday due to the IT outage.
Woolworths NZ director of stores Jason Stockill said the company had been "working all night" with IT operators, including with those in Australia, to resolve the issues.
"The good news is we're fully operational this morning bar online."
He said on Friday the checkout systems went down, and would not start back up even after rebooting them.
"All supermarkets were experiencing the same issues and in several of our stores, too many checkouts went down and we just couldn't operate."
The decision was made to close those affected stores.
"Customers were understanding - it was a global issue and no one was getting too panicked by it."