The malicious software encrypts all the files on a computer then demands a ransom to provide the software key to re-gain access.
It targets Windows systems and has caused big problems in the United States and the United Kingdom.
In Australia and New Zealand, there is about a 2% infection rate.
Netsafe executive director Martin Cocker says the ransoms are demanded in digital currency Bitcoin, that is very difficult to trace.
He advises backing up computer data, having good security software and not clicking on attachments when unsure of their origin.
The cyber-criminals behind the malware are reported to have successfully infected up to 250,000 systems.
The ABC reports the Cryptolocker ransomware works by encrypting a hard drive and the only way to un-encrypt and regain access to the files is to pay a ransom within 72 hours.
If the ransom is not paid, the files are permanently locked with no way of ever accessing them again - though recently the criminals have added a late payment option for a much higher price.