MetService has confirmed visitors to its website in the past few days may have contracted a computer virus from malware hidden in online advertisements on the site.

The state-owned enterprise said it became aware of the issue at 8pm yesterday and immediately shut down the computer server that served up advertisements on its website to prevent more users being infected.

Computer users would not necessarily have needed to click on an advertisement to be infected.

A spokesman initially denied knowledge of the malware when first contacted by The Dominion Post this morning, saying he had not been briefed on any incident

Some computer users reported being infected by a virus called Personal Shield Pro after visiting the MetService site. Most were not initially sure which site had been responsible for the infection. Computer users have been flocking to the MetService website in recent days because of the extreme weather.

Personal Shield Pro is described by security websites as a fake anti-spyware program that logs keystrokes and can be used to obtain passwords and steal money from bank accounts.

MetService marketing manager Jacqui Bridges said its ad server was compromised by a malicious attack, through a vulnerability that allowed someone to upload a binary file into the database.

"This file contained JavaScript code, which redirects the browser to a website which downloads malware files to the client machine,'' she said.

"Over the past week, MetService's website has experienced record numbers of visitors due to the severe weather being experienced across the country. The site has handled this record traffic well. The popularity of the site no doubt made it a target for this attack."

Bridges said the ad server database was being "cleaned and rebuilt".

"We have responded to tweets on the issue starting just before 10am today and will continue to respond to users' concerns as they arise."