Internet users are being warned to make sure computer systems are up to date and data is properly backed up after a new virus that holds data to ransom has hit three victims in New Zealand in the last two weeks.
Cryptolocker first appeared in September and since then it's estimated to have attacked 1000 computers a day in the United States and the United Kingdom.
Unlike other ransomware, which can usually be cleaned up by a technician, the Cryptolocker virus can only be unlocked once a ransom is paid.
Netsafe says about 1000 cases of general ransomware have occurred in New Zealand so far this year and three cases of Cryptolocker have emerged in the last two weeks.
Cyber security programme manager Chris Hails says most of those affected by ransonware infections were using older machines and were running Windows XP.
All three computers infected by the Cryptolocker virus were running on outdated operating systems and two belonged to small businesses.
Mr Hails said one victim lost three months worth of data after payment to the cyber criminals was blocked by the FBI, while the other paid half a bitcoin (about $US400) and successfully got its data back.
The officer in charge of the National Cyber Crime Centre says in most cases where ransom is paid the files are still not unencrypted and he urges people not to pay.
Detective Senior Sergeant Steve Honiss says internet users can avoid being infected by not clicking on attachments to emails and links to websites that they are not 100% sure about.
Netsafe, which helps victims and records data on attacks, advises keeping software up to date and backing up data. "If you've got important family photos or financial information on a computer its always worth keeping an up-to-date backup away from the machine," Mr Hails said.