MetService has confirmed it has been subject to a cyber attack that diverted users of its website to a site downloading malicious software.
The weather agency says the site is now safe to visit, but for about four hours on Tuesday night malware was able to be downloaded through its ad server.
Spokesperson Jacqui Bridges says the attack was probably timed to coincide with high traffic on the website due to this week's extreme weather.
MetService has traced the source of the attack to an overseas computer address, but she doubts this trail will lead it to the culprit.
Ms Bridges says concerned users should check and update their anti-virus software.