The NZX stock exchange is down for the fourth day in a row after a week of cyberattacks.
The site has been targeted by repeated distributed denial of service (DDoS) attacks which began on Tuesday.
A DDoS attack aims to disrupt service by saturating a network with significant volumes of internet traffic.
The site first crashed on Tuesday evening but was up and running shortly after. However this was short lived as it went down again on Wednesday morning then a third time on Thursday.
Professor Dave Parry, from the AUT department of computer science, calls it "a very serious attack on critical infrastructure in New Zealand".
The repeated attacks signal a big problem, he said on Wednesday.
"[It] indicates a level of sophistication and determination which is relatively rare."