SCAMMERS are targeting people at Christmas with emails supposedly from Australia Post that can freeze a computer.
The scam has prompted a warning from the consumer watchdog after more than 100 reports this month.
Australian Competition and Consumer Commissioner deputy chair Delia Rickard said scammers were taking advantage at Christmas time by emailing potential victims about a "missed parcel delivery".
She said the emails purported to be from Australia Post or FedEx and looked like they could be legitimate, despite "fraudulent logos".
"The email may mention a fee will be charged while they hold your undelivered item," she said.
"Scammers ask you to open an attachment or download a file to retrieve your parcel.
"If you follow these instructions, an executable file (.exe) will load onto your computer and install ransomware as soon as it is opened."
She said the ransomware might freeze the computer and demand a fee to unlock it, but there were no guarantees the computer would be unlocked if the ransom was paid.